MEAT, COLD, AND LIGHT. 



sun, it is imagined, makes a great difference in the 

 number of the rays and in the momentum with 

 which they fall on them. So that it has been. 

 thought that Mercury is exceedingly hot, and 

 Georgium Sidus cold beyond conception : but 

 since the Heat produced in- bodies depends on 

 their disposition to receive it, the several planets 

 may be so composed as to- have but a very trifling 

 difference in the Heat produced by the solar rays. 

 Hence, then, what has been hitherto said concern- 

 ing the Heat of the planets as calculated on the 

 -supposition of the sun being the source of Heat, 

 may be called in question : and, perhaps the New- 

 tonian opinion concerning comets (recited in the 

 astronomical part of this work) may in time be 

 entirely abandoned, and some later hypothesis 

 become generally received. 



Thus much for the first method of producing 

 Heat. 



The next method of producing Heat is by ex- 

 citing vibration in solids. Whether fluids can be 

 thus heated, we do not know : there is no clear 

 instance of Heat being produced by their vibration. 

 We may excite vibration in solids, by friction or 

 by collision. If we rub together or strike two 

 bodies, if they have any elasticity they will vibrate. 

 The rougher bodies are which are rubbed together, 

 the greater vibration is produced, and therefore the 

 greater heat. The vibration is also, cat. par. in 

 proportion to the elasticity of bodies. 



Li Count Rumford's ninth Essay, which is an 



inquiry 



