180 FIRE. [Lesson xxvnr. 



to separate the particles of matter ; in which it is 

 opposed by the attraction of cohesion : hence at- 

 traction of cohesion predominating, the body ex- 

 ists in a solid form : caloric existing in such a pro- 

 portion as to weaken the attraction of cohesion to 

 a certain degree, the body assumes a liquid form j 

 and when the quantity of caloric is increased still 

 farther, the body takes a gaseous form. 



That heat moves, like light, with vast velocity, 

 is inferred from caloric being always found to ac- 

 company the rays of light. Dr. Herscheli has dis- 

 covered that the coloured rays of light are pos- 

 sessed of a heating power, and that the least re- 

 frangible rays possess this power in the highest 

 degree : this power diminishing as the refrangi- 

 bility increases j the red rays possessing, therefore, 

 the greatest, and the violet the smallest power. 

 This property is directly opposite, in this respect, 

 to the property which the rays of light possess, of 

 deoxidizing substances exposed to their action 5 

 this property existing in the rays of light, in pro- 

 portion to their degrees of refrangibility. It i* 

 likewise remarkable, that as the deoxidizing power 

 exists, in the highest degree of all, at a certain 

 distance beyond the violet ray, and out of the 

 spectrum, so the calorific power is found to exist, 

 at its maximum, at about half an inch beyond the 

 termination of the spectrum, by the red rays. 



These calorific rays, and which are even regarded 

 as rays of caloric itself, suffer refraction and reflec- 

 tion, similar to the rays of light ; possessing ge- 

 nerally, however, less refrangibility than the rays 



of 



