236 OUTLINES OF NATURAL PHILOSOPHY. 



Short Account of Experiments and Instruments rela- 

 ting to Heat and Moisture^ p. 138., &c. 



330. Water boils with less heat, when the 

 weight of the air diminishes, and, conversely, re- 

 quires a greater heat to make it boil, when the 

 pressure of the air is increased. 



On going to the top of a high mountain, where the 

 weight of the air is diminished by one-tenth, the 

 boiling point of water is somewhat less than 207. 

 So, on going into a deep mine, where the weight of 

 the air is increased by one-thirtieth, the boiling 

 point of water is nearly 214. 



If, by means of the air-pump, the pressure of the air 

 be reduced to one-half, water will boil nearly at the 

 temperature of 180. 



331. The elasticity of the steam generated from 

 water, is measured by the weight that compresses 

 it ; that is, by the weight of the atmosphere pres- 

 sing on the surface of water ; and the relation be- 

 tween this force and the heat required to produce 

 the steam, is expressed by the following exponen- 

 tial equation, where x is the heat measured from 

 the ordinary boiling point, or 212, and f is the 

 force of compression measured in inches of mer- 

 cury, 



v 4 x 



f-m (1.235 ,015' x ~ V^ 



4D / 



This 





