Home About us Products Services Contact us Bookmark
:: wikimiki.org ::
Fahrenheit

Fahrenheit

Fahrenheit is a temperature scale named after the German physicist Gabriel Fahrenheit (1686–1736), who proposed it in 1724. In this scale, the freezing point of water is 32 degrees (this is written "32 °F"), and the boiling point is 212 degrees Fahrenheit, placing the boiling and melting points of water 180 degrees apart. Thus the unit of this scale, a degree Fahrenheit, is 5/9ths of a kelvin (which is a degree Celsius), and minus 40 degrees Fahrenheit is equal to minus 40 degrees Celsius.

History

There are several competing versions of the story of how Fahrenheit came to devise his temperature scale. One states that Fahrenheit established the zero (0 °F) and 100 °F points on his scale by recording the lowest outdoor temperatures he could measure, and his own body temperature. He took as his zero point the lowest temperature he measured in the harsh winter of 1708 through 1709 in his home town of Gdańsk (Danzig) (-17.8 °C). (He was later able to reach this temperature under laboratory conditions using a mixture of ice, ammonium chloride and water.) Fahrenheit wanted to avoid the negative temperatures which Ole Rømer's scale had produced in everyday use. Fahrenheit fixed his own body temperature as 100 °F (normal body temperature is closer to 98.6 °F, suggesting that Fahrenheit was suffering a fever when he conducted his experiments or that his thermometer was not very accurate), and divided his original scale into twelve divisions; later dividing each of these into 8 equal subdivisions produced a scale of 96 degrees. Fahrenheit noted that his scale placed the freezing point of water at 32 °F and the boiling point at 212 °F, a neat 180 degrees apart. Another holds that Fahrenheit established the zero of his scale (0 °F) as the temperature at which an equal mixture of ice and salt melts (some say he took that fixed mixture of ice and salt that produced the lowest temperature); and ninety-six degrees as the temperature of blood (he initially used horse blood to calibrate his scale). Initially, his scale only contained 12 equal subdivisions, but later he subdivided each division into 8 equal degrees ending up with 96. He then observed that plain water would freeze at 32 degrees and boil at 212 degrees. A third well-known version of the story, as described in the popular physics television series The Mechanical Universe, holds that Fahrenheit simply adopted Rømer's scale, at which water freezes at 7.5 degrees, and multiplied each value by 4 in order to eliminate the fractions and increase the granularity of the scale (giving 30 and 240 degrees). He then re-calibrated his scale between the freezing point of water and normal human body temperature (which he took to be 96 degrees); the freezing point of water was adjusted to 32 degrees so that 64 intervals would separate the two, allowing him to mark degree lines on his instruments by simply bisecting the interval six times (since 64 is 2 to the sixth power). His measurements were not entirely accurate, though; by his original scale, the actual freezing and boiling points would have been noticeably different from 32 °F and 212 °F. Some time after his death, it was decided to recalibrate the scale with 32 °F and 212 °F as the exact freezing and boiling points of plain water. This resulted in the healthy human body temperature being 98.6 °F rather than 96 °F. That change was made to easily convert from Celsius to Fahrenheit and vice versa, with a simple formula. This change could also explain why the body temperature once taken as 100 °F by Fahrenheit is today taken by many as 98 °F—because that is a nice, round 37 °C—but more accurately yet in the neighborhood of 98°F. A fourth, not so well-known version of the origin of the Fahrenheit scale depends on Fahrenheit himself being a Freemason (of which there is no definitive evidence). In Freemasonry, there are 32 degrees of enlightenment, 32 being the highest. The use of the 'degree' as well is said to have been derived from the degrees of masonry. This may well be coincidence, but there is no conclusive evidence to the contrary, so the thought persists. In addition, a more humorous but very possible rumor regarding just how Fahrenheit chose his higher temperature involves a not-so-scientific approach to measuring the temperature of a human body. Supposedly, having no human volunteers from which to take his measurement, and not wanting to test it on himself (possibly for lack of an average between several bodies), he decided that the anal temperature of a common pig would closely match the internal body temperature of a human. He proceeded to mark the temperatures of several swine on a mercury tube, found the average, and claimed it to be correct. While the idea of a fairly esteemed scientist taking such a chance with measurement is questionable, given the fact that the body temperature of a pig is very close to that of a human, the logic behind this hasty decision would at least be fairly well placed. It is possible that, in a rush to meet a deadline determined by a boast or otherwise, it was his only option. This is, of course, only a rumor, though it could also account for the slight inaccuracy of Fahrenheit's 100 degree mark being the supposed internal body temperature of a human.

Usage

The Fahrenheit scale was the primary temperature standard for climatic, industrial and medical purposes in most English-speaking countries until the 1960s. In the late 1960s and 1970s the Celsius (formerly centigrade) scale was phased-in by governments as part of the standardizing process of metrication. Fahrenheit supporters claim this is due to Fahrenheit's user-friendliness. The unit of measure, being only 5/9 the size of the Celsius degree, permits more precise communication of measurements without resorting to fractional degrees. Also, the ambient air temperature in most inhabited regions of the world tends not to go far beyond the range of 0 °F to 100 °F: therefore, the Fahrenheit scale would reflect the perceived ambient temperatures, following 10-degree bands that emerge in the Fahrenheit system:
- 10s Deep Frost.
- 20s Light Frost.
- 30s Cold. Close to freezing.
- 40s Cold. Heavy clothing needed.
- 50s Very cool. Moderate Clothing required.
- 60s Cool. Light clothing.
- 70s Comfortable. Summer clothing.
- 80s Warm. Bearable. Minimal clothing.
- 90s Hot.
- 100s Very hot. Take precautions against overheating. However, such a correlation is largely the result of habit: in the same way, Celsius supporters might indicate that 0–10 °C indicates cold, 10–20 °C mild, 20–30 °C warm and 30–40 °C hot, with the minus sign indicating frost. In the United States and Jamaica, where metrication has encountered greater resistance from industry and consumers, the Fahrenheit system continues to be very widely used for this purpose. In most parts of the United Kingdom Celsius has been adopted, although Fahrenheit is still occasionally used by older generations for everyday measurement of higher temperatures, while lower temperatures are more often measured in degrees Celsius. Younger generations in the UK and most other countries have adopted Celsius as the primary scale in use. In Canada, although the media is required to report temperatures in degrees Celsius, many older Canadians still describe temperatures in degrees Fahrenheit. In the United States of America Fahrenheit is popular in medicine too, it is well known that the normal body temperature in Fahrenheit is 98.6 degrees, and easy to remember that a temperature in excess of 100 degrees Fahrenheit requires medical attention. In the rest of the world, body temperature is measured in Celsius as being 37 °C.

Curiosities

The fire point, or kindling point, of paper is 451 °F (233 °C). This is why the title of the book by Ray Bradbury, an American, is Fahrenheit 451.

External links


- [http://www.straightdope.com/classics/a891215.html Alternate story at The Straight Dope] Category:Units of temperature Category:Imperial units Category:Customary units in the United States ko:화씨 ja:華氏

Temperature

Temperature is the physical property of a system which underlies the common notions of "hot" and "cold"; the material with the higher temperature is said to be hotter. Physically, temperature is a measure of the random agitation of matter and ambiant photons, under the effect of thermal fluctuations. It is a fundamental parameter in thermodynamics and it is conjugate to entropy. More quantitatively, the order of magnitude of the fluctuations of the energy associated with an atom, molecule or another elementary constituant of a physical system is k_B T, where k_B is Boltzmann's constant, and T is temperature, expressed in Kelvins.

Overview

The formal properties of temperature are studied in thermodynamics and statistical mechanics. The temperature of a system at thermodynamic equilibrium is defined by a relation between the amount of heat \delta Q incident on the system during an infinitesimal quasistatic transformation, and the variation \delta S of its entropy during this transformation. :\delta S = \frac Contrarly to entropy and heat, whose microscopic definitions are valid even far away from thermodynamic equilibrium temperature can only be defined at thermodynamic equilibrium, or local thermodynamic equilibrium (see below). As a system receives heat its temperature rises, similarly a loss of heat from the system tends to decrease its temperature (at the - uncommon - exception of negative temperature, see below). When two systems are at the same temperature, no heat transfer occurs between them. When a temperature difference does exist, heat will tend to move from the higher-temperature system to the lower-temperature system, until they are at thermal equilibrium. This heat transfer may occur via conduction, convection or radiation (see heat for additional discussion of the various mechanisms of heat transfer). Temperature is also related to the amount of internal energy and enthalpy of a system. The higher the temperature of a system, the higher its internal energy and enthalpy are. Temperature is an intensive property of a system, meaning that it does not depend on the system size or the amount of material in the system. Other intensive properties include pressure and density. By contrast, mass and volume are extensive properties, and depend on the amount of material in the system.

Role of temperature in nature

Temperature plays an important role in almost all fields of science, including physics, chemistry, and biology. Many physical properties of materials including the phase (solid, liquid, gaseous or plasma), density, solubility, vapor pressure, and electrical conductivity depend on the temperature. Temperature also plays an important role in determining the rate and extent to which chemical reactions occur. This is one reason why the human body has several elaborate mechanisms for maintaining the temperature at 37 °C, since temperatures only a few degrees higher can result in harmful reactions with serious consequences. Temperature also controls the type and quantity of thermal radiation emitted from a surface. One application of this effect is the incandescent light bulb, in which a tungsten filament is electrically heated to a temperature at which significant quantities of visible light are emitted. Temperature-dependence of the speed of sound in air c, density of air ρ and acoustic impedance Z vs. temperature °C

Temperature measurement

Main article: Temperature measurement Temperature measurement using modern scientific thermometers and temperature scales goes back at least as far as the early 18th century, when Gabriel Fahrenheit adapted a thermometer (switching to mercury) and a scale both developed by Ole Christensen Rømer. Fahrenheit's scale is still in use, alongside the Celsius scale and the Kelvin scale.

Units of temperature

The basic unit of temperature (symbol: T) in the International System of Units (SI) is the kelvin (K). One kelvin is formally defined as 1/273.16 of the temperature of the triple point of water (the point at which water, ice and water vapor exist in equilibrium). The temperature 0 K is called absolute zero and corresponds to the point at which the molecules and atoms have the least possible thermal energy. An important unit of temperature in theoretical physics is the Planck temperature (1.4 × 1032 K). In the field of plasma physics, because of the high temperatures encountered and the electromagnetic nature of the phenomena involved, it is customary to express temperature in electronvolts (eV) or kiloelectronvolts (keV), where 1 eV = 11,605 K. In the study of QCD matter one routinely meets temperatures of the order of a few hundred MeV, equivalent to about 1012 K. For everyday applications, it is often convenient to use the Celsius scale, in which 0 °C corresponds to the temperature at which water freezes and 100 °C corresponds to the boiling point of water at sea level. In this scale a temperature difference of 1 degree is the same as a 1 K temperature difference, so the scale is essentially the same as the kelvin scale, but offset by the temperature at which water freezes (273.15 K). Thus the following equation can be used to convert from degrees Celsius to kelvins. : \mathrm In the United States, the Fahrenheit scale is widely used. On this scale the freezing point of water corresponds to 32 °F and the boiling point to 212 °F. The following formula can be used to convert from Fahrenheit to Celsius: : \mathrm See temperature conversion formulas for conversions between most temperature scales. ¹ Only the kelvin, Celsius, Fahrenheit, and Rankine scales are in use today.
² Some numbers in this table have been rounded off.
³ Normal human body temperature is 36.8 °C ±0.7 °C, or 98.2 °F ±1.3 °F.

Negative temperatures

:See main article: Negative temperature. For some systems and specific definitions of temperature, it is possible to obtain a negative temperature. A system with a negative temperature is not colder than absolute zero, but rather it is, in a sense, hotter than infinite temperature (sic).

Articles about temperature ranges:


- 10−12 K = 1 picokelvin (pK)
- 10−9 K = 1 nanokelvin (nK)
- 10−6 K = 1 microkelvin (µK)
- 10−3 K = 1 millikelvin (mK)
- 100 K = 1 kelvin
- 101 K = 10 kelvins
- 102 K = 100 kelvins
- 103 K = 1,000 kelvin = 1 kilokelvin (kK)
- 104 K = 10,000 kelvins = 10 kK
- 105 K = 100,000 kelvins = 100 kK
- 106 K = 1 megakelvin (MK)
- 109 K = 1 gigakelvin (GK)
- 1012 K = 1 terakelvin (TK) See Orders of magnitude (temperature).

Theoretical foundation of temperature

Zeroth-law definition of temperature

While most people have a basic understanding of the concept of temperature, its formal definition is rather complicated. Before jumping to a formal definition, let us consider the concept of thermal equilibrium. If two closed systems with fixed volumes are brought together, so that they are in thermal contact, changes may take place in the properties of both systems. These changes are due to the transfer of heat between the systems. When a state is reached in which no further changes occur, the systems are in thermal equilibrium. Now a basis for the definition of temperature can be obtained from the so-called zeroth law of thermodynamics which states that if two systems, A and B, are in thermal equilibrium and a third system C is in thermal equilibrium with system A then systems B and C will also be in thermal equilibrium (being in thermal equilibrium is a transitive relation; moreover, it is an equivalence relation). This is an empirical fact, based on observation rather than theory. Since A, B, and C are all in thermal equilibrium, it is reasonable to say each of these systems shares a common value of some property. We call this property temperature. Generally, it is not convenient to place any two arbitrary systems in thermal contact to see if they are in thermal equilibrium and thus have the same temperature. Also, it would only provide an ordinal scale. Therefore, it is useful to establish a temperature scale based on the properties of some reference system. Then, a measuring device can be calibrated based on the properties of the reference system and used to measure the temperature of other systems. One such reference system is a fixed quantity of gas. The ideal gas law indicates that the product of the pressure and volume (P · V) of a gas is directly proportional to the temperature: : P \cdot V = n \cdot R \cdot T (1) where 'T is temperature, n is the number of moles of gas and R is the gas constant. Thus, one can define a scale for temperature based on the corresponding pressure and volume of the gas: the temperature in kelvins is the pressure in pascals of one mole of gas in a container of one cubic metre, divided by 8.31... In practice, such a gas thermometer is not very convenient, but other measuring instruments can be calibrated to this scale. Equation 1 indicates that for a fixed volume of gas, the pressure increases with increasing temperature. Pressure is just a measure of the force applied by the gas on the walls of the container and is related to the energy of the system. Thus, we can see that an increase in temperature corresponds to an increase in the thermal energy of the system. When two systems of differing temperature are placed in thermal contact, the temperature of the hotter system decreases, indicating that heat is leaving that system, while the cooler system is gaining heat and increasing in temperature. Thus heat always moves from a region of high temperature to a region of lower temperature and it is the temperature difference that drives the heat transfer between the two systems.

Temperature in gases

As mentioned previously for a monatomic ideal gas the temperature is related to the translational motion or average speed of the atoms. The kinetic theory of gases uses statistical mechanics to relate this motion to the average kinetic energy of atoms and molecules in the system. For this case 7736 K = 7463 degrees Celsius corresponds to an average kinetic energy of one electronvolt; to take room temperature (300 K) as an example, the average energy of air molecules is 300/7736 eV, or 0.0388 electronvolt. This average energy is independent of particle mass, which seems counterintuitive to many people. Although the temperature is related to the average kinetic energy of the particles in a gas, each particle has its own energy which may or may not correspond to the average. However, after an examination of some basic physics equations it makes perfect sense. The second law of thermodynamics states that any two given systems when interacting with each other will later reach the same average energy. Temperature is a measure of the average kinetic energy of a system. The formula for the kinetic energy of an atom is:
: K_t = \begin \frac \end mv^2 (Note that a calculation of the kinetic energy of a more complicated object, such as a molecule, is slightly more involved. Additional degrees of freedom are available, so molecular rotation or vibration must be included.)

Thus, particles of greater mass (say a neon atom relative to a hydrogen molecule) will move slower than lighter counterparts, but will have the same average energy. This average energy is independent of the mass because of the nature of a gas, all particles are in random motion with collisions with other gas molecules, solid objects that may be in the area and the container itself (if there is one). A visual illustration of this [http://intro.chem.okstate.edu/1314F00/Laboratory/GLP.htm from Oklahoma State University] makes the point more clear. Not all the particles in the container have different velocities, regardless of whether there are particles of more than one mass in the container, but the average kinetic energy is the same because of the ideal gas law. In a gas the distribution of energy (and thus speeds) of the particles corresponds to the Boltzmann distribution. An electronvolt is a very small unit of energy, approximately 1.602×10-19 joule.

Temperature of the vacuum

When a satellite in empty space is heated by sunshine and cooled by radiating energy away it is not in thermodynamic equilibrium and has no well-defined temperature. A system in a vacuum will radiate its thermal energy, i.e. convert heat into electromagnetic waves. If vacuum is filled with electromagnetic waves (say, radiation from walls of vacuum chamber, or relic microwave radiation in space) then the system will exchange by energy with these waves and thermally equilibrates at some finite (non zero) temperature. Cosmic microwave background radiation being remnant of radiation of hot early universe when radiation was in thermal equilibrium with matter has Planck spectrum (black body spectrum) with the temperature (at present) of about 2.7 K.

Second-law definition of temperature

In the previous section temperature was defined in terms of the Zeroth Law of thermodynamics. It is also possible to define temperature in terms of the second law of thermodynamics, which deals with entropy. Entropy is a measure of the disorder in a system. The second law states that any process will result in either no change or a net increase in the entropy of the universe. This can be understood in terms of probability. Consider a series of coin tosses. A perfectly ordered system would be one in which every coin toss would come up either heads or tails. For any number of coin tosses, there is only one combination of outcomes corresponding to this situation. On the other hand, there are multiple combinations that can result in disordered or mixed systems, where some fraction are heads and the rest tails. As the number of coin tosses increases, the number of combinations corresponding to imperfectly ordered systems increases. For a very large number of coin tosses, the number of combinations corresponding to ~50% heads and ~50% tails dominates and obtaining an outcome significantly different from 50/50 becomes extremely unlikely. Thus the system naturally progresses to a state of maximum disorder or entropy. Now, we have stated previously that temperature controls the flow of heat between two systems and we have just shown that the universe, and we would expect any natural system, tends to progress so as to maximize entropy. Thus, we would expect there to be some relationship between temperature and entropy. In order to find this relationship let's first consider the relationship between heat, work and temperature. A heat engine is a device for converting heat into mechanical work and analysis of the Carnot heat engine provides the necessary relationships we seek. The work from a heat engine corresponds to the difference between the heat put into the system at the high temperature, qH and the heat ejected at the low temperature, qC. The efficiency is the work divided by the heat put into the system or: : \textrm = \frac = \frac = 1 - \frac (2) where wcy is the work done per cycle. We see that the efficiency depends only on qC/qH. Because qC and qH correspond to heat transfer at the temperatures TC and TH, respectively, qC/qH should be some function of these temperatures: : \frac = f(T_H,T_C) (3) Carnot's theorem states that all reversible engines operating between the same heat reservoirs are equally efficient. Thus, a heat engine operating between T1 and T3 must have the same efficiency as one consisting of two cycles, one between T1 and T2, and the second between T2 and T3. This can only be the case if: : q_ = \frac which implies: : q_13 = f(T_1,T_3) = f(T_1,T_2)f(T_2,T_3) Since the first function is independent of T2, this temperature must cancel on the right side, meaning f(T1,T3) is of the form g(T1)/g(T3) (i.e. f(T1,T3) = f(T1,T2)f(T2,T3) = g(T1)/g(T2)· g(T2)/g(T3) = g(T1)/g(T3)), where g is a function of a single temperature. We can now choose a temperature scale with the property that: : \frac = \frac (4) Substituting Equation 4 back into Equation 2 gives a relationship for the efficiency in terms of temperature: : \textrm = 1 - \frac = 1 - \frac (5) Notice that for TC = 0 K the efficiency is 100% and that efficiency becomes greater than 100% below 0 K. Since an efficiency greater than 100% violates the first law of thermodynamics, this implies that 0 K is the minimum possible temperature. In fact the lowest temperature ever obtained in a macroscopic system was 20 nK, which was achieved in 1995 at NIST. Subtracting the right hand side of Equation 5 from the middle portion and rearranging gives: : \frac - \frac = 0 where the negative sign indicates heat ejected from the system. This relationship suggests the existence of a state function, S, defined by: : dS = \frac (6) where the subscript indicates a reversible process. The change of this state function around any cycle is zero, as is necessary for any state function. This function corresponds to the entropy of the system, which we described previously. We can rearranging Equation 6 to get a new definition for temperature in terms of entropy and heat: : T = \frac (7) For a system, where entropy S may be a function S(E) of its energy E, the temperature T is given by: : \frac = \frac (8) The reciprocal of the temperature is the rate of increase of entropy with energy.

See also


- Entropy
- Maxwell's demon
- Heat conduction
- ITS-90 International Temperature Scale

References


-

External links


- [http://www.unitconversion.org/unit_converter/temperature.html Online Temperature Converter] - convert between various units of temperature, such as kelvin, Celsius, Fahrenheit, Rankine, Reaumur, and even Triple point of water
- [http://www.unitconversion.org/unit_converter/temperature-v.html Interactive Temperature Conversion Table] - convert selected unit to all other units of temperature
- [http://www.indiana.edu/~animal/fun/conversions/temperature.html Temperature Conversions: Celsius, Fahrenheit, Kelvin, Réaumur and Rankine]
- [http://www.unidata.ucar.edu/staff/blynds/tmp.html An elementary introduction to temperature aimed at a middle school audience]
- [http://www.straightdope.com/mailbag/mtempscales.html Why do we have so many temperature scales?]
- [http://thermodynamics-information.net A Brief History of Temperature Measurement] Category:Meteorology Category:Physical quantity Category:Thermodynamics Category:Heat ko:온도 ja:温度 th:อุณหภูมิ

Physicist

A physicist is a scientist trained in physics. Physicists study a wide range of physical phenomena spanning all length scales: from the sub-atomic particles from which all ordinary matter is made (particle physics) to the behavior of the material Universe as a whole (cosmology). There are numerous different branches of physics and each has its corresponding specialists, such as astrophysicists, geophysicists, or biophysicists. Employment as a professional physicist generally requires a doctoral degree. Physicists are employed by universities as professors, lecturers, and researchers, and by laboratories in industry. Many people who are trained as physicists, however, use their skills in other parts of the economy, in particular in engineering, computing, and finance.

Astrophysicists and physical cosmologists

At the largest scale, astrophysicists and astronomers study the structure and motion of the universe. This branch of physics is one of the oldest, with its foundations in the ancient study of astronomy. Modern astronomic observation dates from the early 17th century, when Galileo Galilei made the first telescopic observations of the sky. Around the same time period, Tycho Brahe and Johannes Kepler made their careful study of the motion of the planets and comets, laying the groundwork for the first principles of planetary motion. Traditional tools of the astronomer include the telescope, and a device such as the quadrant or sextant to measure elevation. In the 20th century, the radio telescope extended the range of astronomical observation. This expanded range of observation led to the development of physical cosmology, the study of the structure, beginnings, and fate of the cosmos. Two of the more celebrated physicists of the modern age are Edwin Hubble and Steven Hawking. Despite enormous advances in the technology used to make observations of the universe, the majority of astrophysical observation is still a slow and painstaking job.

Particle and quantum physicists

Physicists who deal with the smallest end of the physical universe study particle physics. This is the branch of physics that deals with the structure and ultimate nature of matter. These physicists study particles and phenomena that cannot be seen with the naked eye. To conduct their research, these physicists use particle accelerators and sensitive detecting equipment. Modern particle physics was born when the Danish physicist Niels Bohr first proposed a model for the atom that would explain certain behavior of photon emission. It was soon found that the atom could be split (fission) or combined (fusion). Each process resulted in behavior that could not be explained by Bohr's model of the atom. In the atomic age, Werner Heisenberg and Erwin Schrödinger developed a theory of quantum mechanics to explain the behavior of matter at the smallest scale. Modern physicists are still trying to cope with difficulties introduced by this theory. In particular, it does not fit well with our view of gravity and the universe at the large scale, although it explains the small scale very well. Today's physicists hope to reconcile the two views of the universe some day soon.

See also


- Institute of Physics (UK)
- American Institute of Physics
- List of physicists
- Nobel Prize in physics
- Engineering

External links


- [http://www.bls.gov/oco/home.htm Occupational Outlook Handbook]
- [http://www.bls.gov/oco/ocos052.htm Physicists and Astronomers]; US Department of Labor, Bureau of Labor Statistics ---- ja:物理学者 ko:물리학자 simple:Physicist th:นักฟิสิกส์

1686

Events


- The League of Augsburg is founded.
- Russia, Saxony, Brandenburg and Bavaria join the Holy League against the Ottoman Turkish Empire.
- September 2 The forces of the Holy League of 1684 liberate Buda from the Ottoman Turkish rule that leads to the end of Turkish rule in Hungary during the subsequent years.
- New York City and Albany, New York are granted city charters by the colonial governor.
- A hurricane saves Charleston from attack by Spanish vessels.

Births


- January 16 - Archibald Bower, Scottish historian (d. 1766)
- January 31 - Hans Egede, Norwegian Lutheran missionary (d. 1758)
- April 9 - James Craggs the Younger, English politician (d. 1721)
- April 28 - Michael Brokoff, Czech sculptor (d. 1721)
- April 29 - Peregrine Bertie, 2nd Duke of Ancaster and Kesteven, English statesman (d. 1742)
- May 24 - Gabriel Fahrenheit, German physicist and inventor (d. 1736)
- June 9 - Andrei Osterman, Russian statesman (d. 1747)
- July 6 - Antoine de Jussieu, French naturalist (d. 1758)
- July 9 - Philip Livingston, American politician (d. 1749)
- August 12 - John Balguy, English philosopher (d. 1748)
- August 19 - Eustace Budgell, English writer (d. 1737)
- August 19 - Nicola Porpora, Italian composer (d. 1768)
- October 15 - Allan Ramsay, Scottish poet (d. 1758)

Deaths


- January 31 - Jean Mairet, French dramatist (b. 1604)
- February 10 - William Dugdale, English antiquarian (b. 1605)
- April 6 - Arthur Annesley, 1st Earl of Anglesey, English royalist statesman (b. 1614)
- April 19 - Antonio de Solís y Ribadeneyra, Spanish writer (b. 1610)
- June 23 - William Coventry, English statesman
- July 10 - John Fell, English churchman (b. 1625)
- July 16 - John Pearson, English theologian (b. 1612)
- August 13 - Louis Maimbourg, French-born historian (b. 1610)
- October 26 - John Egerton, 2nd Earl of Bridgewater, English politician (b. 1623)
- November 11 - Louis II de Bourbon, Prince de Condé, French general (b. 1621)
- November 11 - Otto von Guericke, German physicist and inventor (b. 1602) Category:1686 ko:1686년

1724

Events


- January 14 - King Philip V of Spain abdicates the throne
- February 20 - The premiere of Giulio Cesare, an Italian opera by George Frideric Handel, takes place in London
- June 23 - Treaty of Constantinople signed. Partitioned Persia between the Ottoman Empire and Russia
- July 27 - Wild Peter of Hanover captured near Helpensen in Hanover
- November 16 – Jack Sheppard hanged in London
- China expels foreign missionaries
- Blenheim Palace construction is completed. It is presented as a gift to the Duke of Marlborough for his involvement in the Battle of Blenheim in 1704
- Catherine I was named czarina by Peter the Great in Russia
- The Austrian Netherlands agree to the Pragmatic Sanction
- Mahmud of Afghanistan goes insane
- Pierro Orsini becomes Pope Benedict XIII
- Longman, oldest publishing house in England, is founded

Births


- January 24 - Frances Brooke, English writer (d. 1789)
- February 28 - George Townshend, 1st Marquess Townshend, British field marshal (d. 1807)
- April 12 - Lyman Hall, American signer of the Declaration of Independence (d. 1790)
- April 22 - Immanuel Kant, German philosopher (d. 1804)
- April 29 - John Michell, English scientist and geologist (d. 1793)
- May 7 - Dagobert Sigmund von Wurmser, Alsatian-born Austrian general (d. 1797)
- May 19 - Augustus Hervey, 3rd Earl of Bristol, British admiral and politician (d. 1779)
- June 8 - John Smeaton, English civil engineer (d. 1794)
- July 2 - Friedrich Gottlieb Klopstock, German poet (d. 1803)
- July 31 - Noël François de Wailly, French lexicographer (d. 1801)
- August 23 - Abraham Yates, American Continental Congressman (d. 1796)
- August 25 - George Stubbs, English painter (d. 1806)
- August 27 - John Joachim Zubly, Swiss-born Continental Congressman (d. 1781)
- September 3 - Guy Carleton, 1st Baron Dorchester, British soldier and Governor of Quebec (d. 1808)
- October 31 - Christopher Anstey, English writer (d. 1805)
- December 12 - Samuel Hood, 1st Viscount Hood, British admiral (d. 1816)
- December 13 - Franz Aepinus, German scientist (d. 1802)
- December 18 - Louise of Great Britain, queen of Frederick V of Denmark (d. 1751)
- December 24 - Johann Conrad Ammann, Swiss physician and naturalist (d. 1811)
- December 30 - Louis-Jean-François Lagrenée, French painter (d. 1805)

Deaths


- January 6 - Chikamatsu Monzaemon, Japanese dramatist (b. 1653)
- February 12 - Elkanah Settle, English writer (b. 1648)
- March 7 - Pope Innocent XIII (b. 1655)
- May 3 - John Leverett the Younger, American President of Harvard (b. 1662)
- May 21 - Robert Harley, 1st Earl of Oxford and Mortimer, English statesman (b. 1661)
- June 15 - Henry Sacheverell, English churchman and politician (b. 1674)
- October 2 - François-Timoléon de Choisy, French writer (b. 1644)
- October 29 - William Wollaston, English philosophical writer (b. 1659)
- November 16 - Jack Sheppard, English criminal (executed) (b. 1702)
- November 18 - Bartolomeu de Gusmão, Portuguese naturalist (b. 1685) Category:1724 ko:1724년 simple:1724

Water

:This article focuses on water as it is experienced in everyday life. See water (molecule) for information on the chemical and physical properties of pure water (H2O, hydrogen oxide). Water (from the Old English word wæter; c.f German "Wasser", from PIE
- wod-or, "water") is a tasteless, odorless, and nearly colorless (it has a slight hint of blue) substance in its pure form that is essential to all known forms of life and is known also as the most universal solvent. Water is an abundant substance on Earth. It exists in many places and forms. It appears mostly in the oceans and polar ice caps, but also as clouds, rain water, rivers, freshwater aquifers, and sea ice. On the planet, water is continuously moving through the cycle involving evaporation, precipitation, and runoff to the sea. Water fit for human consumption is called potable water. This natural resource is becoming more scarce in certain places as human population in those places increases, and its availability is a major social and economic concern.

Molecular properties

Forms of water

potable water] Water takes many different shapes on earth: water vapor and clouds in the sky, waves and icebergs in the sea, glaciers in the mountain, aquifers in the ground, to name but a few. Through evaporation, precipitation, and runoff, water is continuously flowing from one form to another, in what is called the water cycle. Because of the importance of precipitation to agriculture, and to mankind in general, different names are given to its various forms: while rain is common in most countries, other phenomena are quite surprising when seen for the first time. Hail, snow, fog or dew are examples. When appropriately lit, water drops in the air can refract sunlight to produce rainbows. Similarly, water runoffs have played major roles in human history as rivers and irrigation brought the water needed for agriculture. Rivers and seas offered opportunity for travel and commerce. Through erosion, runoffs played a major part in shaping the environment providing river valleys and deltas which provide rich soil and level ground for the establishment of population centers. Water also infiltrates the ground and goes into aquifers. This groundwater later flows back to the surface in springs, or more spectacularly in hot springs and geysers. Groundwater is also extracted artificially in wells. Because water can contain many different substances, it can taste or smell very differently. In fact, humans and other animals have developed their senses to be able to evaluate the drinkability of water: animals generally dislike the taste of salty sea water and the putrid swamps and favor the purer water of a mountain spring or aquifer.

Water in biology

From a biological standpoint, water has many distinct properties that are critical for the proliferation of life that set it apart from other substances. Water carries out this role by allowing organic compounds to react in ways that ultimately allows replication. It is a good solvent and has a high surface tension, and thus allows organic compounds and living things to be transported in it. Fresh water has its greatest density at 4°C, then becoming less dense as it freezes or heats up from this point. As a stable, polar molecule prevalent in the atmosphere, it plays an important atmospheric role as an absorber of infrared radiation, crucial in the atmospheric greenhouse effect without of which, the average surface temperature would be −18° Celsius. Water also has an unusually high specific heat, which plays many roles in regulating global and regional climate, such as the Gulf Stream climate, allowing life to survive. Water is a very good solvent, chemically not unlike ammonia, and dissolves many types of substances, such as various salts and sugar, and facilitates their chemical interaction, which aids complex metabolisms. Some substances, however, do not mix well with water, including oils and other hydrophobic substances. Cell membranes, composed of lipids and proteins, take advantage of this property to carefully control interactions between their contents and external chemicals. This is facilitated somewhat by the surface tension of water. Water drops are stable due to the high surface tension of water caused by the strong intermolecular forces called cohesive forces. This can be seen when small quantities of water are put onto a nonsoluble surface such as polythene: the water stays together as drops. On extremely clean glass the water may form a thin film because the molecular forces between glass and water molecules (adhesive forces) are stronger than the cohesive forces. This property plays a key role in plant transpiration. A simple but environmentally important and unique property of water is that its common solid form, ice, floats on the liquid. This solid phase is less dense than liquid water, due to the geometry of the strong hydrogen bonds which are formed only at lower temperatures. For almost all other substances and for all other 11 uncommon phases of water ice except ice-XI, the solid form is more dense than the liquid form. Fresh water is most dense at 4°C, and will sink by convection as it cools to that temperature, and if it becomes colder it will rise instead. This reversal will cause deep water to remain warmer than shallower freezing water, so that ice in a body of water will form first at the surface and progress downward, while the majority of the water underneath will hold a constant 4°C. This effectively insulates a lake floor from the cold. While this behavior may seem obvious, even intuitive, it should be noted that almost all other chemicals are denser as solids than they are as liquids, and freeze from the bottom up. Life on earth has evolved with and adapted itself to the important features of water. The existence of abundant liquid, vapor and solid forms of water on Earth has been an important factor in the abundant colonization of Earth's various environments by life-forms adapted to those varying and often extreme conditions. Civilizations have historically flourished around rivers and major waterways; Mesopotamia, the so-called cradle of civilization, is situated between two major rivers. Large metropolises like London, Paris, New York, and Tokyo owe their success in part to their easy accessibility via water and the resultant expansion of trade. Islands with safe water ports, like Singapore and Hong Kong, have flourished for precisely this reason. In places such as North Africa and the Middle East, where water is scarcer, access to clean drinking water was and is a major factor in human development.

Astronomical position of Earth and impact on its water

Mesopotamia The coexistence of the solid, liquid, and gaseous phases of water on Earth is vital to the origin, evolution, and continued existence of life on Earth. However, if the Earth's location in the solar system were even marginally closer or further from the Sun (ie, a million miles or so), the conditions which allow the three forms to be present simultaneously would be far less likely to exist. Earth's mass allows gravity to hold an atmosphere. Water vapor and carbon dioxide in the atmosphere provides a greenhouse effect which helps maintain a relatively steady surface temperature. If Earth were less massive, a thinner atmosphere would cause temperature extremes preventing the accumulation of water except in polar ice caps (as on Mars). According to the solar nebula model of the solar system's formation, Earth's mass may be largely due to its distance from the Sun. The distance between Earth and the Sun and the combination of solar radiation received and the greenhouse effect of the atmosphere ensures that its surface is neither too cold nor too hot for liquid water. If Earth were more distant, most water would be frozen. If Earth were nearer to the Sun, its higher surface temperature would limit the formation of ice caps, or cause water to exist only as vapor. In the former case, the low albedo of oceans would cause Earth to absorb more solar energy. In the second case, a runaway greenhouse effect and inhospitable conditions similar to Venus would result. It has been proposed that life itself may maintain the conditions that have allowed its continued existence. The surface temperature of Earth has been relatively constant through geologic time despite varying solar flux, indicating that a dynamic process governs Earth's temperature via a combination of greenhouse gases and surface or atmospheric albedo. This proposal is known as the Gaia hypothesis.

Human uses of water

Gaia hypothesis All known forms of life depend on water. Water is a vital part of many metabolic processes within the body. Significant quantities of water are used during the digestion of food. (Note however that some bacteria and plant seeds can enter a cryptobiotic state for an indefinite period when dehydrated, and come back to life when returned to a wet environment) About 72% of the fat free mass of the human body is made of water. To function properly the body requires between one and seven litres of water per day to avoid dehydration, the precise amount depending on the level of activity, temperature, humidity, and other factors. It is not clear how much water intake is needed by healthy people. However, for those who do not have kidney problems, it is rather difficult to drink too much water, but (especially in warm humid weather and while exercising) dangerous to drink too little. People do often drink far more water than necessary while exercising, however, putting them at risk of water intoxication, which is frequently fatal. The "fact" that a person should consume eight glasses of water per day cannot be traced back to a scientific source. However, leading dieticians and nutritionists will tell you that this is the RDI (Recommended Daily Intake) of water. [http://ajpregu.physiology.org/cgi/content/full/283/5/R993]. The latest dietary reference intake report by the National Research Council recommended 2.7 liters of water total (including food sources) for women and 3.7 liters for men[http://www.iom.edu/report.asp?id=18495]. Water is lost from the body in urine and feces, through sweating, and by exhalation of water vapor in the breath. Humans require water that does not contain too much salt or other impurities. Common impurities include chemicals and/or harmful bacteria, such as crypto sporidium. Some solutes are acceptable and even desirable for perceived taste enhancement and to provide needed electrolytes.

Water as a precious resource

:See water resources for information about fresh water supplies. fresh water Because of the growth of world population and other factors, the availability of drinking water per capita is shrinking. The issue of water shortage can be solved through more production, better distribution and less waste of it. For this reason, water is a strategic resource for many countries. Many battles and wars, such as the Six-Day War in the Middle East, have been fought to gain access to it. Experts predict more trouble ahead because of the world's growing population, increasing contamination through pollution, and global warming. UNESCO's World Water Development Report (WWDR, 2003) from its World Water Assessment Program indicates that, in the next 20 years, the quantity of water available to everyone is predicted to decrease by 30%. 40% of the world's inhabitants currently have insufficient fresh water for minimal hygiene. More than 2.2 million people died in 2000 from diseases related to the consumption of contaminated water or drought. In 2004, the UK charity WaterAid reported that a child dies every 15 seconds due to easily preventable water-related diseases. Some have predicted that clean water will become the "next oil", making Canada, with this resource in abundance, possibly the richest country in the world.

Regulating water distribution

Drinking water is often collected at springs or extracted from artificial borings in the ground, or wells. Building more wells in adequate places is thus a possible way to produce more water assuming the aquifers can supply an adequate flow. Other water sources are the rainwater and river or lake water. This surface water, however, must be purified for human consumption. This may involve removal of undissolved substances, dissolved substances and harmful microbes. Popular methods are filtering with sand which only removes undissolved material while chlorination and boiling kill harmful microbes. Distillation does all three functions. More advanced techniques exist, such as reverse osmosis. Desalination of abundant ocean or seawater is a more expensive solution used in coastal arid climates. The distribution of drinking water is done through municipal water systems or as bottled water. Governments in many countries have programs to distribute water to the needy at no charge. Others argue that the market mechanism and free enterprise are best to manage this rare resource, and to finance the boring of wells or the construction of dams and reservoirs. Reducing waste, that is using drinking water only for human consumption, is another option. In some cities, such as Hong Kong, sea water is extensively used for flushing toilets citywide in order to conserve fresh water resources. Polluting water may be the biggest single misuse of water; to the extent that a pollutant limits other uses of the water, it becomes a waste of the resource, regardless of benefits to the pollutor. Pharmaceuticals consumed by humans often end up in the waterways and can have detrimental effects on aquatic life if they bioaccumulate and if they are not biodegradable.

The impact of water on human culture

Water is considered a purifier in most religions, including Christianity, Islam, Judaism, and Shinto. For instance, baptism in Christian churches is done with water. In addition, a ritual bath in pure water is performed for the dead in many religions including Judaism and Islam. In Islam, the daily Salah can only be done after ablution (Wodoo), that is, washing parts of the body in clean water. In Shinto, water is used in almost all rituals to cleanse a person or an area. Water is often believed to have spiritual powers. In Celtic mythology, Sulis is the local goddess of thermal springs; in Hinduism, the Ganga is also personified as a goddess. Alternatively, gods can be patrons of particular springs, river or lakes: for example in Greek and Roman mythology, Peneus was a river god, one of the three thousand Oceanids. The Greek philosopher Empedocles held that water is one of the four classical elements along with fire, earth and air, and was regarded as the ylem, or basic stuff of the universe. Water was considered cold and moist. In the theory of the four bodily humours, water was associated with phlegm. Water was also one of the Five Elements in traditional Chinese philosophy, along with earth, fire, wood, and metal. A common misconception about water is that it is a powerful conductor of electricity. Any electrical properties observable in water are due to the ions of mineral salts and carbon dioxide dissolved in it. Water does self-ionize (two water molecules become one hydroxide anion and one hydronium cation), but only at a very slight, almost immeasurable level. Pure water can also be electrolized into oxygen and hydrogen gases but without any dissolved ions, this is a very slow process and thus very little current is conducted. Many bottled water companies exploit another common misconception, advertising both purity and taste, even though pure water is tasteless.

See also


- Dehydration
- Desalination
- Dihydrogen monoxide hoax
- Double distilled water
- Drought
- Ecohydrology
- Evapotranspiration
- Flood
- Flume
- Fountain
- Fresh water
- Heavy water
- Holy water
- Hydrography
- Hydrology
- Irrigation
- Mineral water
- Precipitation (meteorology)
- Rain
- Sea water
- Spring water
- Transvasement
- Wastewater
- WaterAid
- Water (molecule)
- Water industry
- Water ionizer
- Water quality
- Water quality modelling
- Water resources
- World Ocean Day
- World Water Day

External links


- [http://www.lsbu.ac.uk/water/phase.html Phase diagrams of water]
- [http://www.publicforuminstitute.org/issues/oceans/index.htm Oceans and Water Issues Page]
- [http://www.greenfacts.org/water-disinfectants/index.htm Scientific Facts on Water disinfectants] A faithful summary by GreenFacts of a leading scientific consensus report on Drinking Water Disinfectants published by the International Programme on Chemical Safety of the WHO.
- [http://www.hkc22.com/residentialwater.html Residential water problems and markets] Study paper from Helmut Kaiser Consultancy
- [http://www.hkc22.com/watermarketsworldwide.html Water markets worldwide] Study paper from Helmut Kaiser Consultancy
- [http://www.worldwaterforum.org/ World Water Forum]
- [http://www.unesco.org/water/wwap/ World Water Assessment Program]
- [http://unesdoc.unesco.org/images/0012/001295/129556e.pdf United Nations' World Water Development Report]
- [http://www.gemswater.org/ United Nations GEMS/Water Programme]
- [http://www.lsbu.ac.uk/water/ Water Structure and Behaviour]
- [http://www.wateraid.org/ WaterAid]
- [http://www.sahra.arizona.edu/newswatch/ SAHRA—Global Water Newswatch]
- [http://www.siwi.org/ Stockholm International Water Institute] (SIWI)
- [http://www.c-win.org/ California Water Impact Network (C-WIN)]
- [http://news.bbc.co.uk/2/hi/science/nature/3752590.stm BBC: The water debate]
- [http://www.geocities.com/tapvsbottled/ Tap Water Vs Bottled Water] - Interesting site providing facts about tap and bottled water.
- [http://www.emagazine.com/september-october_2003/0903feat1.html E the Environmental Magazine piece on bottled water] (Oct 2003).
- [http://www.iapws.org/ International Association for the Properties of Water and Steam]
- [http://ga.water.usgs.gov/edu/watercycle.html US Geological Survey: Comprehensive discussion of the water cycle, in many languages]
- [http://www.dartmouth.edu/~etrnsfer/water.htm Why is water blue?]
- [http://www.water.org.uk/home/resources-and-links/water-for-health/ask-about/adults Water requirements in adults]
- [http://www.hkc22.com/environmentaltechnology.html/ Climate change raises markets for environmental technology, drinking water and clean energies]

References


- OA Jones, JN Lester and N Voulvoulis, Pharmaceuticals: a threat to drinking water? TRENDS in Biotechnology 23(4): 163, 2005
- Category:Beverages Category:Hydrology Category:Materials Category:Natural resources Category:Nutrition zh-min-nan:Chúi als:Wasser ko:물 ja:水 ms:Air simple:Water th:น้ำ

1 E2 K

To help compare different orders of magnitude this page lists temperatures between 100 kelvins and 1000 kelvins.
- Temperatures lower than 100 K Circumstances where man can stay for a while without special shelter are shown with grey.
- Temperatures higher than 1000 K

External link


- [http://www.ex.ac.uk/trol/scol/index.htm Conversion Calculator for Units of TEMPERATURE] Category:Orders of magnitude (temperature) ja:1 E2 K

Kelvin

The kelvin (symbol: K) is the SI unit of temperature, and is one of the seven SI base units. It is defined as the fraction 1/273.16 of the thermodynamic temperature of the triple point of water. A temperature given in kelvins, without further qualification, is measured with respect to absolute zero, where molecular motion stops. It is also common to give a temperature relative to the reference temperature of 273.15 K, approximately the melting point of water under ordinary conditions; this convention is the Celsius temperature scale. The kelvin is named after the British physicist and engineer William Thomson, 1st Baron Kelvin; his barony was in turn named after the River Kelvin, which runs through the grounds of the University of Glasgow.

SI multiples

Typographical conventions

The word kelvin as an SI unit is correctly written with a lowercase k (unless at the beginning of a sentence), and is never preceded by the words degree or degrees, or the symbol °, unlike degrees Fahrenheit, or degrees Celsius. This is because the latter are adjectives, whereas kelvin is a noun. It takes the normal plural form by adding an s in English: kelvins. When the kelvin was introduced in 1954 (10th General Conference on Weights and Measures (CGPM), Resolution 3, CR 79), it was the "degree Kelvin", and written °K; the "degree" was dropped in 1967 (13th CGPM, Resolution 3, CR 104). Note that the symbol for the kelvin unit is always a capital K and never italicised. There is a space between the number and the K, as with all other SI units. Unicode includes the "kelvin sign" at U+212A (in your browser it looks like K). However, the "kelvin sign" is canonically decomposed into U+004B, thereby seen as a (preexisting) encoding mistake, and it is better to use U+004B (K) directly.

Conversion factors

Kelvins and Celsius

The Celsius temperature scale is now defined in terms of the kelvin, with 0 °C corresponding to 273.15 kelvins.
- kelvins to degrees Celsius
- : \mathrm = \mathrm - 273.15

Temperature and energy

In a thermodynamic system, the energy of the particles of a perfect gas is proportional to the absolute temperature, where the constant of proportionality is the Boltzmann constant. As a result, it is possible to determine the average kinetic energy \overline of the gas particles at the temperature T or to calculate the temperature of the gas from the average kinetic energy of the particles: : \overline = \frac \cdot k_B \cdot \mathrm

See also


- ITS-90 International Temperature Scale

External link


- [http://www1.bipm.org/en/si/si_brochure/chapter2/2-1/2-1-1/kelvin.html BIPM brochure on the kelvin] Category:SI base units Category:Units of temperature ko:켈빈 ja:ケルビン simple:Kelvin th:เคลวิน

Body temperature

Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when temperature surrounding is very different. This process is known as homeostasis: a dynamic state of stability between an animal's internal environment and its external environment (the study of such processes in zoology has been called ecophysiology or physiological ecology). Whereas an organism that thermoregulates is one that keeps its temperature constant and adapts to the temperature of the environment, a thermoconformer changes its body temperature according to the temperature outside of its body. It was not until the introduction of thermometers that any exact data on the temperature of animals could be obtained. It was then found that local differences were present, since heat production and heat loss vary considerably in different parts of the body, although the circulation of the blood tends to bring about a mean temperature of the internal parts. Hence it is important to determine the temperature of those parts which most nearly approaches to that of the internal organs. Also for such results to be comparable they must be made in the same situation. The rectum gives most accurately the temperature of internal parts, or in women and some animals the vagina, uterus or bladder. Occasionally that of the urine as it leaves the urethra may be of use. More usually the temperature is taken in the mouth, axilla or groin.

Temperature regulation

# conduction - heat escapes from your body when you sit on a cold rock. # convection - cooler air currents remove heat from the surface of your skin. # evaporation - evaporative cooling occurs when water (often from perspiration) leaves the skin surface as a gas, lowering the body temperature by taking the heat of evaporation from the body. # radiation - e.g. acquisition of heat from solar radiation (e.g. snakes "sunning" on a cold day).

Types of thermoregulation

There are two types of thermoregulation that are used by animals: #physiological regulation: This is when an organism changes its physiology to regulate body temperature. For example, our body tends to sweat inorder to cool our body down. Another example is when our bodies get cold, it likes to shiver so that the body can create some heat. #behavorial regulation: This is when an organism changes its behavior to change its body temperature. For example, when your body starts to get hot because of the sun, you may want to find a shade to cool yourself down.

Physiological temperature regulation in vertebrates

By numerous observations upon men and animals, John Hunter showed that the essential difference between the so-called warm-blooded and cold-blooded animals lies in the constancy of the temperature of the former, and the variability of the temperature of the latter. Those animals high in the scale of evolution, as birds and mammals, have a high temperature almost constant and independent of that of the surrounding air, whereas among the lower animals there is much variation of body temperature, dependent entirely on their surroundings. There are, however, certain mammals which are exceptions, being warm-blooded during the summer, but cold-blooded during the winter when they hibernate; such are the hedgehog, bat and dormouse. John Hunter suggested that two groups should be known as "animals of permanent heat at all atmospheres" and "animals of a heat variable with every atmosphere," but later Bergmann suggested that they should be known as "homeothermic" and "poikilothermic" animals. But it must be remembered there is no hard and fast line between the two groups. Also, from work done by J. O. Wakelin Barratt, it has been shown that under certain pathological conditions a warm-blooded (homeothermic) animal may become for a time cold-blooded (poikilothermic). He has shown conclusively that this condition exists in rabbits suffering from rabies during the last period of their life, the rectal temperature being then within a few degrees of the room temperature and varying with it. He explains this condition by the assumption that the nervous mechanism of heat regulation has become paralysed. The respiration and heart-rate being also retarded during this period, the resemblance to the condition of hibernation is considerable. Again, Sutherland Simpson has shown that during deep anaesthesia a warm-blooded animal tends to take the same temperature as that of its environment. He demonstrated that when a monkey is kept deeply anaesthetized with ether and is placed in a cold chamber, its temperature gradually falls, and that when it has reached a sufficiently low point (about 25 °C in the monkey), the employment of an anaesthetic is no longer necessary, the animal then being insensible to pain and incapable of being roused by any form of stimulus; it is, in fact, narcotized by cold, and is in a state of what may be called "artificial hibernation." Once again this is explained by the fact that the heat-regulating mechanism has been interfered with. Similar results have been obtained from experiments on cats. These facts—with many others—tend to show that the power of maintaining a constant temperature has been a gradual development, as Darwin's theory of evolution suggests, and that anything that interferes with the due working of the higher nerve-centres puts the animal back again, for the time being, on to a lower plane of evolution.

Ectotherms

Main article: Ectotherm Even though fishes are ectotherms some have developed the ability to remain functional even when the water temperature is below freezing and some even use natural antifreeze to resist ice crystal formation in their tissues; amphibians (also ectotherms) must cope with the loss of heat through their moist skins by evaporative cooling; reptiles, like amphibians must warm their bodies by behavioral adaptations; the stratum corneum they possess limits heat loss by evaporative cooling.

Endotherms

Main article: Endotherm Birds avoid overheating by panting since, unlike the mammals, their thin skin has no sweat glands. Down feathers trap warm air acting as excellent insulators (sometimes used by humans). Hair in mammals also acts as a good insulator; mammalian skin is much thicker than that of birds and often has a continuous layer of insulating fat beneath the dermis - in marine mammals like whales this is referred to as blubber.

Heat production in birds and mammals

In cold environments, birds and mammals can compensate for heat loss by: # utilizing small smooth muscles (arrector pili in mammals) which are attached to feather or hair shafts; this shivering thermogenesis distorts the surface of the skin as the feather/hair shaft is made more erect (called goose bumps or pimples). # animals in cold climates tend to be larger (easier to maintain core body temperature) than similar species in warmer climates. # be capable of storing energy as fat for metabolism # have reduced extremities # some have countercurrent blood flow in extremities (e.g. timber wolves) to avoid freezing of tissues. In warm environments, birds and mammals avoid overheating by: # behavioral adaptations like living in burrows during the day and being nocturnal # evaporative cooling by perspiration and panting # storing fat reserves in one place (e.g. camel's hump) to avoid its insulating effect # elongate, often vascularized extremities to conduct body heat to the air.

Behavioral temperature regulation

In addition to human beings, a number of animals also maintain their body temperature by physiological and behavioral adjustments. For example, a desert lizard is an ectotherm and is therefore unable to control its temperature through metabolic regulation. However, by altering its location continuously, it is able to maintain a crude form of temperature control. In the morning only its head will emerge from its burrow. Later the entire body is exposed. The lizard basks in the sun, aborbing solar heat. When the temperature reaches higher levels, the lizard will hide under rocks or return to its burrow. When the sun goes down or the temperature falls, it emerges again. Some animals living in cold environment maintain their body temperature by preventing heat loss. Their fur grows more dense to increase the insulation. Some arctic animals are able to allow their less insulated extremities to cool to temperatures much lower than their core temperature -- nearly to 0 °C. This minimizes heat loss through less insulated body parts, like the legs, feet (or hooves), and nose.

Hibernation estivation and daily torpor

Rather than cope with limited food resources and low temperatures, some mammals "punt" in a sense by hibernating in underground burrows; in order to remain in "stasis" for long periods these animals must build up brown fat reserves and be capable of slowing all body functions; True hibernators (e.g. groundhogs) keep their body temperature down throughout their hibernation while the core temperature of false hibernators (e.g. bears) varies with them sometimes emerging from their dens for brief periods; bats are true hibernators which rely upon a rapid, nonshivering thermogenesis of their brown fat deposit to bring them out of hibernation. Estivation occurs in summer (like siestas) and allows some mammals to survive periods of high temperature and little water (e.g. turtles burrow in pond mud). Daily torpor occurs in small endotherms like bats and humming birds which temporarily reduce their high metabolic rates to conserve energy.

Variations in the temperature of man and some other animals

core temperature As stated above, the temperature of warm-blooded animals is maintained with but slight variation. In health under normal conditions the temperature of man varies between 36 °C and 38 °C, or if the thermometer be placed in the axilla, between 36.25 °C and 37.5 °C In the mouth the reading would be from 0.25 °C to 1.5 °C higher than this; and in the rectum some 0.9 °C higher still. The temperature of infants and young children has a much greater range than this, and is susceptible of wide divergencies from comparatively slight causes. Of the lower warm-blooded animals, there are some that appear to be cold-blooded at birth. Kittens, rabbits and puppies, if removed from their surroundings shortly after birth, lose their body heat until their temperature has fallen to within a few degrees of that of the surrounding air. But such animals are at birth blind, helpless and in some cases naked. Animals who are born when in a condition of greater development can maintain their temperature fairly constant. In strong, healthy infants a day or two old the temperature rises slightly, but in that of weakly, ill-developed children it either remains stationary or falls. The cause of the variable temperature in infants and young immature animals is the imperfect development of the nervous regulating mechanism. The average temperature falls slightly from infancy to puberty and again from puberty to middle age, but after that stage is passed the temperature begins to rise again, and by about the eightieth year is as high as in infancy. A diurnal variation has been observed dependent on the periods of rest and activity, the maximum ranging from 10 a.m. to 6 p.m., the minimum from 11 p.m. to 3 a.m. Sutherland Simpson and J.J. Galbraith have recently done much work on this subject. In their first experiments they showed that in a monkey there is a well-marked and regular diurnal variation of the body temperature, and that by reversing the daily routine this diurnal variation is also reversed. The diurnal temperature curve follows the periods of rest and activity, and is not dependent on the incidence of day and night; in monkeys which are active during the night and resting during the day, the body temperature is highest at night and lowest through the day. They then made observations on the temperature of animals and birds of nocturnal habit, where the periods of rest and activity are naturally the reverse of the ordinary through habit and not from outside interference. They found that in nocturnal birds the temperature is highest during the natural period of activity (night) and lowest during the period of rest (day), but that the mean temperature is lower and the range less than in diurnal birds of the same size. That the temperature curve of diurnal birds is essentially similar to that of man and other homoiothermal animals, except that the maximum occurs earlier in the afternoon and the minimum earlier in the morning. Also that the curves obtained from rabbit, guinea pig and dog were quite similar to those from man. The mean temperature of the female was higher than that of the male in all the species examined whose sex had been determined. Meals sometimes cause a slight elevation, sometimes a slight depression—alcohol seems always to produce a fall. Exercise and variations of external temperature within ordinary limits cause very slight change, as there are many compensating influences at work, which are discussed later. Even from very active exercise the temperature does not rise more than one degree, and if carried to exhaustion a fall is observed. In travelling from very cold to very hot regions a variation of less than one degree occurs, and the temperature of those living in the tropics is practically identical with those dwelling in the Arctic regions.

Limits compatible with life

There are limits both of heat and cold that a warm-blooded animal can bear, and other far wider limits that a cold-blooded animal may endure and yet live. The effect of too extreme a cold is to lessen metabolism, and hence to lessen the production of heat. Both catabolic and anabolic changes share in the depression, and though less energy is used up, still less energy is generated. This diminished metabolism tells first on the central nervous system, especially the brain and those parts concerned in consciousness. Both heart-beat and respiration-number become diminished, drowsiness supervenes, becoming steadily deeper until it passes into the sleep of death. Occasionally, however, convulsions may set in towards the end, and a death somewhat similar to that of asphyxia takes place. In some experiments on cats performed by Sutherland Simpson and Percy T. Herring, they found them unable to survive when the rectal temperature was reduced below 16 °C. At this low temperature respiration became increasingly feeble, the heart-impulse usually continued after respiration had ceased, the beats becoming very irregular, apparently ceasing, then beginning again. Death appeared to be mainly due to asphyxia, and the only certain sign that it had taken place was the loss of knee jerks. On the other hand, too high a temperature hurries on the metabolism of the various tissues at such a rate that their capital is soon exhausted. Blood that is too warm produces dyspnoea and soon exhausts the metabolic capital of the respiratory centre. The rate of the heart is quickened, the beats then become irregular and finally cease. The central nervous system is also profoundly affected, consciousness may be lost, and the patient falls into a comatose condition, or delirium and convulsions may set in. All these changes can be watched in any patient suffering from an acute fever. The lower limit of temperature that man can endure depends on many things, but no one can survive a temperature of 45 °C (113 °F) or above for very long. Mammalian muscle becomes rigid with heat rigor at about 50° C., and obviously should this temperature be reached the sudden rigidity of the whole body would render life impossible. H.M. Vernon has done work on the death temperature and paralysis temperature (temperature of heat rigor) of various animals. He found that animals of the same class of the animal kingdom showed very similar temperature values, those from the Amphibia examined being 38.5 °C, Fishes 39 °C, Reptilia 45 °C, and various Molluscs 46 °C. Also in the case of Pelagic animals he showed a relation between death temperature and the quantity of solid constituents of the body, Cestus having lowest death temperature and least amount of solids in its body. But in the higher animals his experiments tend to show that there is greater variation in both the chemical and physical characters of the protoplasm, and hence greater variation in the extreme temperature compatible with life.

Reference

:Textbook of Physiology, Kirkes, (Philadelphia, 1907) Category:animal physiology

Ice

] Ice is the solid form of water. The phase transition occurs when liquid water is cooled below 0 °C (273.15 K, 32 °F) at standard atmospheric pressure. An unusual feature of ice frozen at a pressure of one atmosphere is that the solid is some 8% less dense than liquid water. Ice has a density of 0.917 g/cm³ at 0 °C, whereas water has a density of 0.9998 g/cm³ at the same temperature. Liquid water is most dense, essentially 1.00 g/cm³, at 4 °C and becomes less dense as the water molecules begin to form the hexagonal crystals of ice as the temperature drops to 0 °C. (In fact, the word "crystal" derives from the Greek word for frost.) This is due to hydrogen bonds forming between the water molecules, which line up molecules less efficiently (in terms of volume) when water is frozen. The result of this is that ice floats on liquid water, an important factor in Earth's climate. When ice melts, it absorbs as much heat energy (the heat of fusion) as it would take to heat an equivalent mass of water by 80 °C, while its temperature remains a constant 0 °C. As a crystalline solid, ice is considered a mineral.

Types of ice

mineral Everyday ice and snow is hexagonal ice (ice Ih). Subjected to higher pressures and varying temperatures, ice can form in roughly a dozen different phases. Only a little less stable (metastable) than Ih is cubic structure ice (Ic). But cooling Ih causes a different arrangement to form in which the protons move, XI. With both cooling and pressure more types exist, each being created depending on the phase diagram of ice. These are II, III, V, VI, VII, VIII, IX, and X. With care all these types can be recovered at ambient pressure. The types are differentiated by their crystalline structure, ordering and density. There are also two metastable phases of ice under pressure, both fully hydrogen disordered, these are IV and XII. Ice XII was discovered in 1996. As well as crystalline forms solid water can exist in amorphous states as amorphous solid water (ASW), low density amorphous ice (LDA), high density amorphous ice (HDA), very high density amorphous ice (VHDA) and hyperquenched glassy water (HGW). Kurt Vonnegut's novel Cat's Cradle features Ice IX as a central element of the plot, although real Ice IX does not have the properties of Vonnegut's fictional ice-nine (i.e. the ability to freeze all water on Earth with the introduction of one granule). Rime is a type of ice formed by fog freezing on cold objects. It contains a high proportion of trapped air, making it appear white rather than transparent, and giving it a density about one quarter of that of pure ice. Ice can also form icicles, similar to stalactites in appearance, as water drips and re-freezes. Clathrate hydrates are forms of ice that contain gas molecules trapped within its crystal lattice. Pancake ice is a formation of ice generally created in areas with less calm conditions. Some other substances (particularly solid forms of those usually found as fluids) are also called "ice": dry ice, for instance, is a popular term for solid carbon dioxide. carbon dioxide, circa 1905.]]

Human relationship with ice

carbon dioxide, Iran, built during the Middle Ages for storing harvested ice.]] Ice has long been valued as a means of cooling. Until recently, the Hungarian Parliament building used ice harvested in the winter from Lake Balaton as its primary source of energy for air conditioning. Icehouses were used to store ice during the winter so as to preserve perishables during the summer, and