ON THE NATURE OF HEAT. 25/ 



susceptibility) heat be communicoted, its temperature may 

 remain unaltered ; a greater power, or longer application of ~ 

 vibration, being now necessary to occasion a temperature, 

 which, before the susceptibility for vibration was diminished, 

 was produced by a power much smaller, or an application 

 much shorter. Hence steam is no hiii;ber in temperature steam, 

 than boilino^ .water. If, during this change of susceptibi- 

 lity for vibration, no farther application of heat be made, 

 it follows, that the temperature must fall : hence arise the Freezing mix*^ 

 effects of freezing mixtures. lures. 



It scarcely need be added, that the converse of all this Corverieof 

 will take phice, if the susceptibility for vibration be increased, 

 and no abstract on of heat be made. The temperature then 

 must rise; for the body contains within itself what may be 

 termed the power of vibration ; a given quantity of which 

 produces a greater inteni^ity of vibration in any body, ac- 

 cording to the susceptibility of that body for vibration. 



Such is an iii\perfect sketch of the hypothesis of vibration, 

 which 1 proposed to give. Many circumstances, which 

 would have elucidated, and perhaps have confirmed the opi- 

 nions, have been necessarily omitted ; and here the greatest 

 candour of your readers will be constantly required. 



It may be useful in concluding, to present a summary of Summary, 

 the circumstances which have been considered; and thus to 

 institute a comparison between the two hypotheses. 



1st, The tirft principles of each opinion are equally hy- The tt/o hypo* 

 pothetical. the.es com- 



j r . ... . pared. 



2dly, The production of heat by friction is explained by 



the hypothesis we propose; but not, satisfactorily at least, 

 by the other. 



3dly, Certain facts have been related, under the head of 

 the eft'ects of heat, which appear to afford fome degree of 

 contmdiction to the hypothesis of material caloric; and 

 although they may not be easily explained on the opposite 

 principle, yet they do not by any means appear contradic- 

 tory to it. 



The advantages of our theory appear most conspicuous 

 in the following particulars; for 



4thly, The properties of good conductors, and of good 

 radiators of caloric, are explaiiicd by it alone. 



5thly, 



