touching his Theory of Light and Colours, 201 



tend out of the rarer medium into the denser; and in that 

 case therefore the reflexion having a double cause ought to be 

 stronger than in the aether, as it is apparently. But in refrac- 

 tion this rigid tenacity or unpliableness of the superficies need 

 not be considered, because so much as the ray is thereby bent 

 in passing to the most tenacious and rigid part of the superfi- 

 cies, so much is it thereby unbent again in passing on from 

 thence through the next parts gradually less tenacious. 



Thus may rays be refracted by some superficies and re- 

 flected by others, be the medium they tend into denser or 

 rarer. But it remains further to be explained, how rays alike 

 incident on the same superficies (suppose of crystal, glass or 

 water), may be at the same time, some refracted, others re- 

 flected ; and for explaining this, I suppose that the rays when 

 they impinge on the rigid resisting aetherial superficies, as they 

 are acted upon by it, so they react upon it, and cause vibra- 

 tions in it, as stones thrown into water do in its surface, and 

 that these vibrations are propagated every way into both the 

 rarer and denser mediums as the vibrations of air which cause 

 sound are from a stroke, but yet continue strongest where they 

 began, and alternately contract and dilate the aether in that 

 physical superficies. For it's plain by the heat which light 

 produces in bodies that it is able to put their parts in motion, 

 and much more to heat and put in motion the more tender 

 aether, and it's more probable that it communicates motion to 

 the gross parts of bodies by the mediation of aether than im- 

 mediately ; as, for instance, in the inward parts of quicksilver, 

 tin, silver, and other very opake bodies, by generating vibra- 

 tions that run through them, than by striking the outward 

 parts only without entering the body. The shock of every 

 single ray may generate many thousand vibrations, and by 

 sending them all over the body, move all the parts, and that 

 perhaps with more motion than it could move one single part 

 by an immediate stroke; for the vibrations, by shaking each 

 particle backward and forward, may every time increase its 

 motion, as a ringer does a bell by often pulling it, and so at 

 length move the particles to a very great degree of agitation, 

 which neither the simple shock of a ray nor any other motion 

 in the aether, besides a vibrating one, could do. Thus in air 

 shut up in a vessel, the motion of its parts caused by heat, 

 how violent soever, is unable to move the bodies hung in it 

 with either a trembling or progressive motion ; but if air be 

 put into a vibrating motion by beating a drum or two, it 

 shakes glass windows, the whole body of a man, and other 

 massy things, especially those of a congruous tone; yea, I 

 have observed it manifestly shake under my feet a cellared 



Phil. Mag. S. 3. Vol. 29. No. 193. Sept. 1 846. P 



