164? GOtfNT RUMTOHD^S NEW EXPERIMENTS 



friclion againft the end of the cylinder immerfed in the boi 

 ing water, I occafioned all the thermometers to rife feveral 

 degrees. 

 The difference It-may perhaps be imagined, at fir ft fight of the refults of 



between the ex- . * ? ... 



periment and the t,,e experiment, that, as the three thermometers, which occu* 

 theory confirm pied the parts about the middle of the axis of the cylinder, did 

 pot indicate a decreafe perfectly agreeing with the theory, the 

 theory itfelf cannot be true: but a moment's reflection wilt 

 fhow, that this inference would be too hafty, and that the dif- 

 ference between the theory and the refults of our experiments, 

 far from proving any thing adverfe to the theory, ferve on the 

 contrary to render it more probable, 

 becaufe the The refults of fuch experiments can never agree with the 



thermometers ttteorv > except (he divifions of our thermometers be perfectly 

 are defective. accurate: but it is well known to every one, who has any 

 knowledge of natural philofophy, that the divifions of our ther- 

 mometers are defective. 

 To improve this One. of the objects I had in view in the experiments, of 

 ©"btaTnm'or" wmch * have juft fe»*n an account to. the clafs, and in feveral 

 tance. others, which I intend to make without delay, is to improve 



the divifion of the fcale of the thermometer, in order to render 

 this valuable inftrument of greater utility in the delicate in- 

 veftigations of natural philofophy. 

 The air thermo- It appears certain, that the increafe of the elaflicity of air 

 t^b* «. TT ky heat is much more nearly proportionate to the increafe of 

 to. temperature, than the dilatation of mercury or any known 



fluid ; confequently it is the air thermometer we ought to en- 

 deavour to improve, and which mud ultimately afford us the 

 moft accurate meafure of heat, that it is poffible for us to 

 procure. 



Sect. IV. The Heat produced in a Body by a given Quantity 

 offular Light is the fame whether the Bays be denfer or rarer t 

 convergent, parallel, or divergent. 



Whether the In all cafes where the rays of the fun flrike on the fur face 



quantity °f heat f a n opake body without being reflected, heat is generated, 

 the folar rays be and the temperature of the body is increafed : but is the 

 proportional to quantity of heat thus excited always in proportion to the quan- 

 forbed. *• ili y °f n £ nt tnat ^ as difappeared ? This is a very interesting 

 queftion, and has not hitherto found a deciiive folution. 



When 



