2 g SPECIFIC HEAT. PART i. 



centigrade thermometer, even if the capacity of our 

 faa ^planet for heat were as low as that of water ; it would 

 therefore be mostly reduced to vapour, and should the 

 earth then fall to the sun as it certainly would do, the 

 quantity of heat developed by striking on the sun would 

 be 400 times greater. It is even supposed that the light 

 and heat of the sun are owing to showers of bodies 

 falling on the surface with impetus proportionate to his 

 attraction, for had he been in combustion he would have 

 been burnt out ages ago. The masses of meteoric iron 

 and stone that occasionally fall on the earth show that 

 matter may be wandering in space; the vast zone of 

 smaller bodies that in their annual revolutions round 

 the sun come within the earth's attraction in August 

 and November, when thousands of them take fire and are 

 consumed on entering our atmosphere, show that a great 

 amount of matter of small dimensions exists within our 

 own system. Much may be beyond it which drawn by 

 the sun's attraction may fall on his surface. 



When a body is heated, it absorbs one part of the 

 heat; the other part raises its temperature. The part 

 absorbed increases the bulk or volume of the body, the 

 expansion being the exact measure, or mechanical equi- 

 valent of the heat absorbed. In fact the coefficient of 

 expansion is the fractional part of the expansion in 

 length, surface, or volume of the body when its tem- 

 perature is raised one degree. When the body is 

 cooled, its volume is diminished, and then the contrac- 

 tion is an exact measure, or mechanical equivalent of 

 the heat given out, and thus expansion and contraction 

 are correlatives with and represent heat and cold. 



Specific heat is the quantity of heat required to raise 

 a given bulk or a given weight of a body a given num- 

 ber of degrees. In the one case it is distinguished as 

 the specific heat for a constant volume, in the other for 

 a constant weight. 



