12 VETEKINAKY OPHTHALMOLOGY. 



affair, being composed of seven colors, — violet, indigo, 

 blue, green, yellow, orange and red. One may demon- 

 strate this by vising a triangular piece of glass — a 

 prism — and intercepting a beam of light, which will be 

 split up into its component parts, the red rays being 



Fig. 9. 



Diagram illustrating the decomposition, in passing through a prism, of 

 white light into the seven colors of the spectrum (Biclard) : r, red » 

 o, orange ; j, yellow ; v. green ; . b, blue ; i, indigo ; vi, violet. 



refracted the least and the violet the most. It is not 

 the province of a small compilation, such as is repre- 

 sented by this little work, to give full details in the 

 physiology of sight. That must be culled from your 

 various text-books on physiology. That point at whibh 

 the image is focused on the retina is called the " field of 

 projection." Here the visual purple becomes bleached 



