1894.] Atmospheric Temperature, especially during Fohn. 125 



discussing; by taking account of the rapidity of their movement 

 they can be constructed to give the temperature inferentially. The 

 only probable method of observing directly such rapid changes of 

 temperature is by electric or thermoelectric methods. A thermo- 

 electric junction is made of metals which conduct the heat rapidly, 

 and as their mass can be made very small and their specific heat is 

 low they can be made to follow the temperature of the medium in 

 which they are immersed more closely than any other form of ther- 

 mometric apparatus. The galvanometer necessary for measuring the 

 currents produced is the inconvenient part of the apparatus, but I am 

 informed by those familiar with such apparatus that a suitable instru- 

 ment for use in the field could be constructed without difficulty. 



Thermometers as Calorimeters. If we know not only the rate of 

 cooling of a thermometer, if we have the figure which, in Leslie's 

 language, is called the "range," and if in addition we know the 

 thermal mass of the bulb which is generally expressed by its " water 

 value," the thermometer becomes an efficient calorimeter. It is a 

 familiar observation that the thermometer and the senses frequently 

 disagree about the warmth or coldness of the weather. This is 

 because they measure different things. The thermometer measures 

 the temperature of the air, the senses measure the heating or cooling 

 power of the atmosphere, or the rate at which the body is called upon 

 to receive or supply heat. The body is a calorimeter and not a nere 

 thermometer. But with a knowledge of the constants above men- 

 tioned, the thermometer becomes also a calorimeter. 



In connection with the melting of ice by the hot wind in the 

 Engadin, and the corresponding abstraction of heat from the air, I 

 made a number of experiments by whirling thermometers at various 

 speeds in air of definite temperature, having previously warmed the 

 thermometer to a higher temperature. 



In order to give calorimetric expression to the result, and to express 

 the heat exchange which had taken place, it was necessary to know 

 the water value or thermal mass of the thermometer bulb. In similar 

 experiments made by Leslie, he used a tin sphere 4 in. in diameter 

 filled with water, of which it contained more than half a litre, and 

 there was no difficulty in finding the ^thermal mass, as that of the 

 thermometer was an insignificant fraction of it. With a mercurial 

 thermometer, however, of ordinary type the glass envelope of the 

 bulb is as important from a calorimetric point of view as the mercury 

 contained in it ; and it is impossible to know the proportions in 

 which the two substances are present, except by weighing them in 

 process either of construction or of destruction. The former of these 

 processes was excluded, and I hesitated to adopt the latter before 

 some more use had been got out of the thermometer. Meantime I 

 endeavoured to estimate the probable thermal mass of the bulb by 



