100 CALORIC THE ACTIVE PRINCIPLE IN LIGHT. 



3. That the electric spark (like that produced 

 by the collision of flint and steel) consists of ex- 

 ceedingly minute portions of ponderable matter 

 in a state of incandescence, as will be shown 

 hereafter by the decisive and beautiful experi- 

 ments of Fusinieri. 



4. That when the electric fluid is transmitted 

 through the vacuum of an air pump, little or no 

 light is produced, as proved by the experiments 

 of De Luc, and afterwards by those of Sir H. 

 Davy. 



5. That the most intense heat of a voltaic 

 battery never produces any light, except when 

 acting on ponderable matter ; consequently, that 

 light and heat are not identical,* as maintained 

 by some modem theorists ; and that neither of 

 them is generated by the mere vibrations of an 

 aethereal medium. 



* That caloric is a constituent of light, (as it is of all other 

 bodies,) and is the active principle in its generation, is evident 

 from the fact, that the most refractory gems and metals are 

 transformed into luminous incandescent particles by a sufficiently 

 intense heat, definite measures of which are required to produce 

 the effect on different species of matter. It has also been proved 

 by the experiments of Hulme, Dessaignes, Macartney, and others, 

 that every species of phosphorescence is promoted (for a time) 

 by moderate heat, and always extinguished by the coldness of 

 freezing mixtures; while others have found that the light of 

 luminiferous insects is much greater in vessels of oxygen gas than 

 in common air. But that caloric is a distinct essence, and may 

 exist independent of light, is manifest from the fact, that it con- 

 verts solids into liquids, vapours, and gases, in the midst of per- 

 fect darkness ; while it radiates from the earth during night, as 

 it does from boiling liquids and other hot bodies, without being 

 attended with any light. 



