Refracted and Diffracted Liyht. 425 



just described, it is not restored to its former state, as it 

 -would be in passing through a second prism of equal refrac- 

 tive power, in an opposite direction ; because in the for- 

 mer case, with the usual arrangement, as well as in the 

 present experiment, the light least refracted by the first 

 object, is least exposed to the highest degree of refraction 

 from the second ; and this must necessarily produce the 

 separation of the light into distinct images in the experi- 

 ment, with the candle, and produce those intervals in the 

 other experiments, which lead to a developement of the 

 fringes. 



Many other appearances, which have hitherto been 

 among the mysteries of the science, may be traced to the 

 same principle ; the unequal refraction of light, before 

 unequally refracted, and indebted for its colourless state 

 to a system of mutual compensations, must frequently 

 produce colours, either directly, by disturbing the order of 

 the arrangement, or indirectly, by producing intervals for 

 the developement. 



The dark lines observed when light is admitted through 

 a narrow aperture, may be accounted for upon this prin- 

 ciple ; and when the light, thus admitted, is dispersed by 

 subsequent refraction, these lines ought to appear in the 

 different colours of the spectrum ; but if they are the same 

 lines which have been observed by Fraunhotfer, and other 

 philosophers, how they became fixed, is a question which 

 the present state of our knowledge has not prepared us to 

 answer: the fact is unconnected, by analogy or otherwise, 

 with any known phenomena to aid us in its explanation. 



The refraction of common light is always accompanied 

 by partial reflexion ; and as the attraction of the edges of 

 bodies, or the refraction arising from it, accounts for the 

 inflexion of a part of the transmitted light towards the 

 body, so the attendant reflexion accounts for the deflexion 

 of another part from it ; and we may thus account for the 

 principal -phenomena of diffracted light, without the as- 

 sumption of forces, unconnected with any other object, 

 and without deviating from the usual simplicity of nature. 



I am fully persuaded that the effects of refraction, traced 

 upon known and admitted principles, are quite suflicieut 

 to account for the greater part of those appearances which 



