Temperature

Temperature. One of the simplest sensations which we experience is that of heat but our sense of heat is by no means trustworthy. One person may consider a room to be hot, another may say it is cold, and the same person may regard a body as hot or cold, according to his condition. We can arrange certain bodies of different degrees of hotness in a series so that they form a rising scale, and in this way we are comparing them one with another. This, however, would not be very definite; we should not be able to say how much hotter one body was than another. When, however, we have managed to measure the hotness of a body by reference to some standard, we are in a position to speak of its temperature. Bodies of different hotness will exchange heat when in each others' presence - the hotter ones cool while the cooler ones get hotter. When no further exchange of heat takes place they are said to be at the same temperature. Thus the temperature of a body can be measured if we know the temperature of another body which is in thermal equilibrium with it. The temperature of this standard body is measured by means of one of the effects which are produced in it by heat. 0ne of the most obvious effects of heat is to cause expansion, and so bodies which expand greatly with heat are chosen as standards of reference, If a bulb of glass containing mercury is connected to a tube of fine uniform bore, the mercury will rise in the tube as it is heated more and more. We might then say that equal differences of temperature shall be taken to mean those which produce equal elongations of the mercury column. An arbitrary scale of temperature would then be obtained. But suppose we took a perfectly different liquid from mercury - say, alcohol - and fixed our scale with reference to its expansion only, we should find the two scales did not agree. If the mercury be taken to expand regularly, then equal differences of temperature measured by it do not produce equal elongations in the column of alcohol. Other liquids show similar variations. Which, then, is to be taken as a true standard? Which is to be considered as expanding regularly? This was a problem of considerable importance, and has only been satisfactorily settled in modern times. It is found that all perfect gases agree among themselves, and hence the expansion of one of these has been adopted as a standard - e.g. in the air thermometer. A perfectly independent scale of temperature has, howevEr, been evolved from thermodynamical reasoning; a scale whose absolute zero (-273° of the Centigrade thermometer) corresponds to that given by the air thermometer, and therefore justifies the trust which had been placed in the latter. [THERMODYNAMICS.]