Light. 147 



in a point and cross each other: and the sooner 

 they cross each other, after passing the crystal- 

 line lens, the larger will be the inverted image 

 painted on the retina. The visual angle, there- 

 fore, is that which is made by two right lines 

 drawn from the extreme points of any object to 

 the eye ; and on the measure of that angle the 

 apparent magnitude of every visible object will 

 depend/ 



20. The prism used by opticians is a piece of 

 fine glass, in form of, a geometrical triangular 

 prism ; it has the power of separating the rays of 

 light. 



