62 TITE REASON WHY. 



** So teach us to number our days, that we may apply our hearts unto wisdom.' 

 PSALM xc. 



326. Wliy does water become steam ? 



Because a larger amount of heat has entered into it than can 

 remain latent in water. The water therefore expands and rises in 

 the form of vapour, or water attenuated by heat. 



327. Sow many degrees of Tieat are latent, or hidden, in 

 the different states of water ? 



In thawing ice, 140 deg. of caloric become latent ; and in 

 converting the water into steam, 1,000 deg. more of caloric are 

 be taken up. Therefore, ice requires to take up 1,140 deg. of latent 

 caloric before it becomes steam. 



328. What is the most modern theory of heat ? 



It is this that caloric, which produces heat, is an extremely 

 subtile fluid, of so refined a nature that it possesses no weight, yet 

 is capable of diffusing itself among the particles of the most solid 

 bodies. 



It is also believed that all bodies are subject to the action of 

 two opposing forces : one, the mutual attraction of their particles ; 

 the other, the repulsive force of caloric and that bodies exist in 

 the aeriform, fluid, or solid state, according to the predominance 

 of either the one or the other of these opposing forces. 



329. How do we measure the quantity of caloric in any 

 substance ? 



It is impossible to determine the amount of caloric which any 

 body contains. Our sensations would obviously be deceptive, since, 

 if we dipped the right hand in snow, and held the left hand before 

 the fire, and then immersed both hands in cold water, the water 

 would feel warm to the right hand and cold to the left hand. 



But, as caloric uniformly expands substances that are under its 

 influence, one of the bodies most sensitive to calorific effects has 

 been selected to be the indicator of the amount of caloric. This 

 substance is quicksilver ; and the scale of measurement, and the 

 apparatus for exhibiting the rise or fall of the quicksilver, consti- 

 tute the thermometer. 



330. If it is impossible to measure the amount of caloric in 

 any substance, how can it be said that ice absorbs 140 deg. iv 

 becoming water ? 



