CHEM-J6TRY. 



33 



bent towards the perpendicular: when it passes from a dense 

 to a rarer medium, it is turned from the perpendicular. 



Light is a compound of seven colors, viz : violet, indigo, blue, 

 green, yellow, orange and red. The colors can be separated 

 by a triangular piece of glass, called a prism : they possess 

 different degrees of refrangibility, as will be seen by the 



Fig. 1. Solar Spectrum. 



figure. 



Violet 



Indigo 



Blue 



Green 



Yellow 



Orange 



Red 



[This cut shows the solar spectrum in the order of its seven colors : 

 the violet appears most, and the red least refracted.] 



There are also heating rays, which attend the luminous 

 ones: the calorific, or heating powers of the red rays, are the 

 greatest : these powers diminish in the order of the spectrum, 

 from the red to the violet, which possesses the least of all. 

 Light is a powerful decomposing agent : many chemical com- 

 pounds, as the salts of silver, are decomposed by the agency 

 of light alone. The influence of light on vegetation is very 

 important, and will be noticed hereafter. The process of 

 taking phtographic and Daguerreotype pictures, depends upon 

 the action of light on a sensitive metallic surface. 



There are several sources of light : the great source of light 

 which produces the day to our earth, is the sun, the moon's 

 light is only a reflected light which it receives from the sun. 

 The combustion of bodies is another source of light : another 

 form of light is called phosphoresence, which is emitted by 

 certain bodies, as phosphorus, decayed wood, putrid flesh, 



