Temperature
the thermal condition of a body which determines the interchange of heat between it and other bodies. Our first ideas of temperature are derived from our sensations of hot and cold. The effect of adding heat to a body is to make it hotter, unless it is at its melting or boiling point. This rise of temperature is accompanied by volume changes, on which all our practical methods of measuring temperature depends. Now, though the idea of temperature is familiar enough, its true significance is difficult to understand. Socalled thermometric measurements of temperature are not measurements in the strict scientific sense of the term.
They are simply the comparison of certain other effects which accompany change of temperature in special bodies.
A scientific measure of temperature should be independent of any particular substance, and should depend solely on the fundamental properties of heat itself. This absolute measure of temperature was first given by Lord Kelvin (Sir W. Thomson), who based his system on Carnot's thermodynamic cycle. The kinetic theory of gases has given us a definition of temperature in terms of the kinetic energies of the molecules. The assumption is that the molecules are free from molecular forces; the conclusion is in agreement with Boyle's, Gay-Lussac's, and Charles's laws. As no gas obeys these laws rigorously, the inference is that intermolecular actions come into play, so that only part of the temperature can be expressed in terms of the kinetic energies of the molecules. The same is true, but in a much greater degree, for liquids and solids, for which as yet no kinetic theory has been formulated.
From experiments made by Kelvin and Joule, the absolute zero of temperature was found to be 274 centigrade degrees below the freezing point of water, or -461° F. This agrees almost exactly with the value deduced from the kinetic theory of gases. From our present standpoint, therefore, we cannot expect to get a colder temperature. The coldest natural temperature hitherto registered on the earth's surface is -88.8° F., which was observed in January, 1886, at Verkhoyansk in Siberia (lat. 67° 34′ N. and lon. 133° 51' E.). Olszewski has, in his experiments on the liquefaction of the gases, measured temperatures as low as -373° F. by means of a hydrogen thermometer.
Guesses have been made from time to time as to the temperature of space, a In meteorology the distribution of atmospheric temperature is one of the most important problems calling for discussion. The mean annual temperature over the whole surface of land and sea is perhaps about 45° F. At Verkhoyansk the lowest monthly mean averages-61.2° F. The highest monthly mean averaged over several years may be set down at fully 110° F., and is experienced in the N. W. parts of India, where the thermometer in free shaded air not unfrequently touches 125° F. Loomis in his "Meteorology" gives 133° F. as the highest authentic reading, made in the Great Desert of Africa. To facilitate the study of the distribution of temperature at the earth's surface, it is usual to construct charts of isotherms. These are lines, each of which is drawn through all places having the same mean monthly, mean seasonal or mean annual temperature.
The periodic changes of atmospheric temperature are due to the sun. The earth itself has, however, a distinct temperature, which increases at the rate of 1° F. for every 50 or 60 feet of descent through the few miles of crust accessible to us. On this real earth temperature the mean annual temperature of the air must to a large extent depend. one TEMPERATURE OF THE BODY.
The terms cold-blooded and warm-blooded animals serve roughly to indicate, the former, those animals which possess a temperature little raised above that of the surrounding medium; the latter, those with considerably higher.
Fishes, frogs, and reptiles are cold-blooded animals, while birds and quadrupeds are warm-blooded. Heat is produced through the combination of the oxygen of the atmosphere with the carbon and hydrogen of the blood and tissues. A much larger quantity of carbon and hydrogen is added to the blood from the food than the ordinary nutrition of the body demands; and the oxygen inhaled from the atmosphere, uniting with these elements, produces heat, carbonic acid, and water-the latter products representing the ashes of the bodily fire. Thus the temperature of the living body depends on chemical change. It is produced by the oxidation of combustible materials derived from the tissues and from the blood. The quantity of carbon and hydrogen which in any given period unite with oxygen in the body, may be ac- TEMPERATURE counted for by the quantity of heat generated in the same period. The temperature of an animal must thus be proportionate to its respiration, and to the activity and frequency of its breathing movements.
The circumstances which influence the temperature of the human body in health are very varied. The normal temperature of the internal parts varies from 98.5 to 99.5. The average temperature of the armpit is 98.6. In infant life the temperature is about 1° F. above that of the adult; and the temperature of old age resembles that of infancy. The temperature of the female slightly exceeds that of the male; and the temperature of the human body falls to its lowest level in the early morning. The influence of disease on temperature is very marked. In typhus fever and pneumonia the temperature may rise to 106° F. On the side of lowness of temperature may be mentioned cases of morbus cœruleus, in which the blood is imperfectly ærated, when the temperature may sink to 77.5° F.