44 HEAT OR CALORIC. 



phori, it vanishes instantly, and leaves no trace behind all i- 

 darkness. 



(b.) Light can be entirely excluded. Although it seems to pene- 

 trate and enter all bodies, it shines through none but those that are 

 called transparent or translucent. 



(c.) Heat can be partially imprisoned. When the sources from 

 which it flows are intercepted, its effects do not instantly vanish, but 

 decline gradually. 



(d.) Heat cannot be entirely excluded. It makes its way, more or 

 less rapidly, through all kinds of matter. 



EFFECTS OF HEAT, OR CALORIC, AND PRINCIPAL DIVISIONS OF 



THE SUBJECT. 



Certain effects on the form, and other properties and powers of bod- 

 ies, are observed to arise from the addition and abstraction of heat. 

 They may be embraced under 

 I. Expansion, 

 II. Distribution of temperature, 



III. Congelation and liquefaction, 



IV. Vaporization and gazification, 

 V. Natural evaporation, 



VI. Ignition, 



VII. Capacity for heat Specific Heat, 

 VIII. Combustion. 



APPENDIX. 



The sources of heat and cold. 



I. EXPANSION. 



1. By expansion, is intended an increase of the three corporeal 

 dimensions, length, breadth and thickness. Contraction is of course 

 the opposite of this. 



(a.) The entrance of heat into a body produces the same result, 

 in regard to its dimensions, as if more matter were added to it. 



(6.) The abstraction of heat gives, in this respect, the same re- 

 sult, as if matter were taken from the body all around. 



Swelling and shrinking, then, are produced by heating and cooling. 



(c.) The absolute weight of a body is not altered, if the weight be 

 estimated in vacuo ; but if it be weighed in any surrounding medi- 

 um, whose density does not vary during the experiment, the specific 

 gravity of the body will be found to change with the temperature. 



(c?.) The experiments are supposed to be conducted at such a 

 temperature as not to produce decomposition. 



2. Bodies in all the three states, solid, fluid and aeriform, are 

 subject to the law of expansion. 



(a.) *fl.s an instance of the expansion of solids, an iron cylinder 

 neatly turned, and fitted to a gauge by which its dimensions are meas- 

 ured, answers very well. Its length is received between two pro- 



