HEAT, COLD, AND LIGHT. 325 



same temperature, without bringing any thing 

 into it eiiher hot or cold, fora very great length of 

 time. 



As to the effects produced by Heat, it is known 

 to expand bodies ; and some late chemists affirm, 

 that it tends to diminish every attraction we are 

 acquainted with: they produce experiments to 

 evince that Heat diminishes the attraction of 

 gravitation, of cohesion, of magnetism, of 

 electricity, and chemical attractions. But though 

 it may be the case in particular instances, it will 

 be better not to be too sanguine in imagining that 

 such effects will take place universally. The asser- 

 tion may be disputed with regard to the attraction 

 of gravitation, and that of electricity. However, 

 those who allow that Heat universally diminishes 

 the electrical attraction, will strongly contend in. 

 support of their opinion, because they may thereby 

 explain with facility the reason of the frequency 

 of thunder-storms in summer. 



From a review of what has been here advanced, 

 we shall find that there are few, or, perhaps, we 

 may confidently say, no appearances, but what 

 will admit of as easy an explanation, by conjec- 

 turing that Heat is a quality, as by supposing that 

 it is a substance. Nay, some of the phenomena, 

 particularly those which attend the production of 

 Heat by friction, or vibration in solids, will (as 

 must appear from what has been previously ob- 

 served) induce us to incline mose to the former 

 hypothesis than to the latter. Besides, whether 

 Heat be a substance, or a quality, it is manifest, 



thai 



