LAW OF REFRACTION. 245 



In the case of refraction that is, the modifying of the 

 course of a ray of light in passing through a transparent 

 substance, instead of being reflected from one that is 

 opaque the law is in itself equally simple, though it is, 

 perhaps, not quite so easily stated. The best way for you 

 to picture it to your minds is perhaps to consider that 

 when a ray enters water, for example, obliquely, it has 

 the mass of the water, or a larger portion of it, in closer 

 proximity to it on one side than on the other at the in- 

 stant of entering / or, as it might perhaps be expressed, 

 it comes sooner in contact, or more fully in contact with 

 it on the side toward which it inclines than on the other 

 side. 



What I mean by this is shown in the diagram, where 

 W 10 represents the water, S S 

 the surface of it, and I o the 

 incident ray. Now, whatev- 

 er may be the nature of the 

 force represented by the ray 

 " s of light, and whatever maybe 

 the action of the water upon 

 it as it passes into the water 

 out of the air, it is easy for us 

 to imagine that, in entering 

 it any point, as at o, it must 

 come sooner, or more fully, under the action of the water 

 which is on the side W, toward which it is inclined at the 

 point of entering, than on the side w,from which it is in- 

 clined. Indeed, in former times, when light was believed 

 to consist 'of solid particles impelled with great velocity 

 through the air, it was thought that the bending of the ray 

 to one side in this case was caused by the more powerful 

 attractive force exerted by the greater mass of water on 

 that side at the instant of entering. At any rate, this idea 



DIAGRAM. LAW OP REFK ACTION. ^V a j 



