gS2 



OPTICS. 



Light is generally considered as a peculiar species 

 of matter which is emitted or sent off in rays 

 from certain bodies, which hence are called lu- 

 minous bodies. 



Light appears to move with a velocity that is 

 truly inconceivable. It arrives at the earth from 

 the sun in seven or eight minutes, which is at the 

 rate of 150,000 miles in a second. The light of a 

 lamp is seen at the distance of several miles appa- 

 rently at the same instant it is lighted, it being 

 impossible to measure so minute a portion of time 

 as that which it occupies in traversing this space. 

 The particles of light must also be minute beyond 

 human imagination, for otherwise, from their 

 amazing velocity, they would impinge on bodies 

 with great force, and our organs of vision would 

 be destroyed by them. 



If a lighted candle be set by night on an emi- 

 nence, it may be seen all round at the distance of 

 half a mile ; wherefore, there is no place within a 

 sphere of a mile in diameter, in which the eye can 

 be placed, where it will not receive some rays from 

 this small flame. 



From the extreme minuteness of the particles of 

 light it is, that they cross each other in all directions 

 without the least apparent disturbance. 



