the received Theory of Newton's Rings. 



459 



dulation, for in this case the vibrations are not reversed. No 

 analogy therefore exists between the theory of Newton's rings 

 heretofore received, and that which explains other phenomena 

 of a similar nature. 



The error is evidently due to the circumstance, that, trust- 

 ing to the accuracy of Newton's observations, the formula of 

 intensity (3.), which applies solely to the case where a rever- 

 sion of the aether vibrations may be assumed, has been ex- 

 tended to the case w r here the distance being 0, no reversion is 

 possible. It may be remarked, further, that the depth has 

 never been introduced into the proportion, nor could it be so 

 introduced, as a fourth proportional infinitely great would be 

 the consequence. It is thus easy to conceive how, neglecting 

 to test the original observations of Newton, the same error 

 might be repeated through centuries. 



With regard, finally, to the origin of the central spot, 

 which by daylight appears black, but by homogeneous light, 

 on account of the dull background, does not appear darker 

 than the rings caused by interference, my opinion coincides 

 with that of Jericau, that the spot is caused by transmitted 

 light in the same manner as the spot upon a mirror when a 

 little of the metallic coating is removed from behind. The 

 part from which the coating has been removed appears dark 

 in comparison with the surrounding bright reflecting surface. 

 I however agree with this notion, not as a probable conjecture, 

 but as an undeniable fact. The grounds of this assertion are 

 the following : — 



Let DEC represent a glass prism, 

 O the place of the eye, and GH a 

 line parallel to the ends. A refrac- 

 tion of red light is first possible at t 

 when the angle O/G is =49° 2', or 

 the angle of incidence at t=4>8° 58'; 

 and a refraction of the violet in q 

 first occurs when the angle O^G 

 = 50° 7', or the angle of incidence 

 = 39° 53'. Let p be the place at 

 which the middle rays are refracted. 

 Between t and BE no ray will be broken at the base DB, and 

 hence in this portion a total reflexion will take place. Be- 

 tween t and p, red, orange and yellow rays can pass through ; 

 and, on account of their absence, the light reflected from this 

 portion will be diminished in intensity. Between p and q all 

 the other rays, blue and violet excepted, are allowed to pass ; 

 here therefore the intensity of the reflected light will be still 

 less, while in the vicinity of q, where the blue and violet have 



