162 ELEMENTARY PROPERTIES 



a beam of solar matter may be reflected and 

 refracted, and either condensed to a focal 

 point, or segregated into parts, and each part 

 produce upon the eye a diversity of impressions. 

 The materiality of the solar rays is fur- 

 ther proved, by the chemical effects pro- 

 duced on different bodies which are exposed 

 to their influence. By their influence, vege- 

 tables, which, in the dark, were pallid and 

 white, are found to recover their natural ver- 

 dure and bloom; by their power, water becomes 

 gassified ; metals calcified ; and other bodies 

 modified and changed to such a degree, that 

 they acquire properties altogether different 

 from those which they before possessed. 



Although the materiality of the solar rays 

 appears to me an incontrovertible truth, the 

 mode by which its effects are produced, has 

 been a source of difference among natural 

 philosophers. HUYGENS, DES CARTES, and 

 EULER, considered light to be a subtile fluid, 

 filling space, and thrown into undulations by the 

 sun ; which undulations extending themselves 

 to the eye, render bodies visible. Sir ISAAC 

 NEWTON, on the contrary, considered light to 

 be a real substance, consisting of small parti- 

 cles, which perpetually emanating, in straight 

 lines, from luminous bodies, and entering the 

 eye, excite the sensation of vision, or the per- 



