404 Mr. Powell on Light and Heat, [June, 



continues to act its natural part without undergoing any alter- 

 ation. 



(8.) (Brande's Chemistry, i. 297, 2d Edit.; Davy's Elements, 

 p. 215.) " Newton has put the query whether light and com- 

 mon matter are not convertible into each other ? and if we con- 

 sider sensible heat in bodies to depend upon vibrations of their 

 particles, a certain intensity of vibrations may send off particles 

 into free space ; and particles moving rapidly in right lines may, 

 in losing their own motion, communicate a vibrating motion to 

 the particles of teri'estrial bodies." 



Without any hypothesis as to the nature of heat, it is obvious 

 that the principle above adopted will readily explain the conver- 

 tibility of common matter into hght, or at least of light existing 

 in a state of material combination, into li^ht in a free radiant 

 state. Whether the light consist of particles of the bodies from 

 which it is generated combined with latent heat, or of peculiar 

 particles entirely of a separate species, at first existing in com- 

 bination with solid matter, and then liberated and brought into 

 the state of luminous elastic fluid by the agency of latent heat, 

 we have probably no means of deciding. It is possible that 

 light may be formed from certain particles of the body which are 

 made to assume a radiant state in a way analog-ous to the forma- 

 tion of vapour ; but the opinion that the light is a peculiar sub- 

 stance in combination with the body from which it is extricated 

 seems to be the more probable one from the fact of the absorp- 

 tion of light by various bodies. 



(Phil. Trans. 1817, Part I. p. 73.) Sir H. Davy has concluded 

 that the luminosity of flames is greater in those cases where 

 solid particles are volatilized and ignited. This is exactly con- 

 formable to the principle here advanced. Solid particles ought 

 to be more readily convertible into light, caleris paribus, than 

 those of elastic fluids. They have less capacity for heat; there- 

 fore of the heat communicated to them, a larger share can go to 

 the evolution of light, and a greater quantity of light is con- 

 densed in the same space. 



Hence it would follow also that the less solid the product the less 

 luminous would the flame be, and therefore the less heat would 

 be employed in producing light, and consequently the more in 

 raising temperature. 



It may arise from the peculiar constitution of bodies, that 

 their heat may in some cases be more employed in producing 

 light, and in others more in increasing temperature or radiating 

 heat : thus the ratio of heat really produced in flames may be 

 very difterent from what appears. 



1 have alluded to the production of light from some particula,r 

 sources only. There are, as is well known, several others from which 

 it is generated, and to these must the examination be extended 

 before we can, strictly speaking, consider the conclusion as 



