36 THEORY OF LIGHT. 



He further observes that " light, heat, and electricity, if not 

 modifications of each other, appear to be members of the same 

 family." See Gurney's Lectures. 



Now, I consider, that to produce heat it is necessary that the 

 elements which constitute light must be ab initio present, and 

 that it is the energy of their action in approximating each other 

 by the particular individual polarity, by which alone they can 

 combine to form the compound particles of light, that the sen- 

 sation called heat producing in all bodies, whether solid, fluid, 

 or gaseous, the needful expansion or rarefaction to liberate the 

 elementary atoms from their position of conjunction or union 

 of poles, appropriate to their then state of fixation ; and that by 

 such liberation the poles of the elementary atoms are definitely 

 placed, relatively in the most favorable position to present the 

 essential poles to form by immediate conjunction perfect light ; 

 that the energy of the sensation of heat (or caloric) is propor- 

 tional to the difficulty of re-solution of the fixed body to the 

 necessary degree of attenuation, and final dissolution of such 

 fixed body to a free uncombined state of its elementary prin- 

 ciples ; in other words, that each original atom is distinctly 

 separated from its former combination, and ready to unite in 

 the new compound of radiant matter or light. 



