16 LIGHT. 



15. THEORY OF VIBRATION. Another 

 What is the view is that the fluid above described does 



other view of 



the nature of not pass from the sun and other luminous 

 objects to the eye, but fills the space be- 

 tween them and serves as a medium for producing the 

 sensation of light, as the air does for producing sound. 

 TJ , . .,. 16. When a bell is struck its vibrations 



Illustrate this 



view ? are communicated to the air, and so to the 



ear, producing the effect of sound. So, according to the 

 view of light last mentioned, vibrations are caused by 

 some means in the sun and certain other bodies, which 

 being rapidly transmitted through the fluid above men- 

 tioned, produce, when they fall on the eye, the sensa- 

 tion of light. 



17. EXISTENCE OF THE SUPPOSED FLUID. 



How is this 



fluid known to Such a fluid as this theory requires is known 

 to exist in the spaces between the heav- 

 enly bodies, by the influence which it exerts on their 

 motions, and is supposed to pervade all substances, whe- 

 ther solid, liquid or gaseous, occupying the spaces be- 

 tween their pores. It is called ether, but has no rela- 

 tion to the chemical and medicinal liquid of the same 

 name. 



18. BOTH VIEWS EXPLAIN THE FACTS. 

 ther view ex- For tne explanation of most of the facts 



^ rac ~ and laws of light it; matters little which 

 view is taken. Thus, it is certainly true 

 that light is reflected from mirrors, whether we suppose 

 it a subtle fluid, and that its reflection is the glancing 

 off of its particles from the polished surface, as a ball 

 thrown obliquely against the side of a house glances 



