THERMO-D YNA MICS. ?>7 



escape, the air does a vast amount of work in creating 

 vortical whirls ; it causes the air that issues to circulate 

 in vortical movements with great velocity, and in order to 

 do this it expends a vast amount of work, and the con- 

 sequence is that the air in doing this working cools to a 

 very great extent, because instead of having work done 

 upon it, it is doing work itself, and in order to do work it 

 must absorb heat, and the heat absorbed is the exact 



equivalent of the work which the gas does. You see the 

 needle move sensibly away to the other side, showing that 

 cold was produced by the work which was being done by 

 the air in issuing from that orifice. There are a very 

 large number of other ways in which heat can be generated 

 without the performance of mechanical work. There is, 

 for example, when chemical combinations take place, a 

 development of heat, although the operator is exerting no 



