LIGHT. 15 



CHAPTER II. 



LIGHT. 

 12. CHEMICAL ACTION OF LIGHT. Da- 



Jn what cases 



does light act guerreotype pictures are produced by the 



chemically? chemical action of light< So Hght actg 



chemically in converting water and irhe carbonic acid 

 of the air into vegetable matter. The action of light 

 in these cases will be explained hereafter. The present 

 chapter is devoted to the consideration of its nature and 

 more important laws. 



13. LIGHT is WITHOUT WEIGHT. While 



wefht? Uffki the effects of tight* and the laws according 

 to which they take place are well under- 

 stood, philosophers differ with respect to its nature. It 

 is, however, agreed that light is imponderable, or without 

 weight, this being inferred from the fact that an illu- 

 mined object weighs no more than the same object 

 when unillumined. 



14. NEWTON'S THEORY. Newton main- 



What is New- . . /i i i 



ton's theory ? tamed that light is a fluid thinner or more 



Nation of sTglt Sllbtle than ^ OT **? ^ but Composed 



produced?- like these of minute particles, constantly 

 given off from the sun and all luminous objects. He 

 supposed that it is this substance passing into the eye 

 that produces the sensation of sight, as the fine particles 

 of fragrant matter, passing off from flowers, produces 

 the sensation of smell. 



