SUPPLEMENT TO A MEMOIR ON THE REFLEXION 

 AND REFRACTION OF LIGHT. 



IN a paper which the Society did me the honour to publish 

 some time ago*, I endeavoured to determine the laws of Re- 

 flexion and Refraction of a plane wave at the surface of separa- 

 tion of two elastic media, supposing this surface perfectly plane, 

 and both media to terminate there abruptly : neglecting also all 

 extraneous forces, whether due to the action of the solid particles 

 of transparent bodies on the elastic medium, which is supposed 

 to pervade their interstices, or to extraneous pressures. I am 

 inclined to think that in the case of non-crystallized bodies 

 the latter cause would not alter the form of our results in the 

 slightest degree ; and possibly there would be some difficulty in 

 submitting the effects of the former to calculation. Moreover, 

 should the radius of the sphere of sensible action of the mole- 

 cular forces bear any finite ratio to \, the length of a wave of 

 light, as some philosophers have supposed, in order to explain 

 the phenomena of dispersion, instead of an abrupt termination 

 of our two media we should have a continuous though rapid 

 change of state of the ethereal medium in the immediate vicinity 

 of their surface of separation. And I have here endeavoured to 

 shew, by probable reasoning, that the effect of such a change 

 would be to diminish greatly the quantity of light reflected at 

 the polarizing angle, even for highly refracting substances : sup- 

 posing the light polarized perpendicular to the plane of inci- 

 dence. The same reasoning would go to prove that in this case 

 the quantity of the reflected light would depend greatly on 

 minute changes in the state of the reflecting surface. I have 

 on the present occasion merely noticed, but not insisted upon, 

 these inferences, feeling persuaded that in researches like the 

 present, little confidence is due to such consequences as are not 

 supported by a rigorous analysis. 



* Supra, p. 243. 



