150 EXPERIMENTS AND INVESTIGATIONS 



constant, we shall get the equation (a being = AE, b = BE, 



and EC = a?) y = : , also a wholly dif- 



V^-i-^- Jb* + a* 



ferent curve from the conic hyperbola, which all experiments 

 give. Therefore the conclusion from the whole is that the 

 phenomena have no reference to interference. 



Having delivered the doctrines Vesulting from these experi- 

 ments, I have some few particulars to add, both as illustrating 

 and confirming the foregoing propositions, as removing one or 

 two difficulties which have occurred to others until they were 

 met by facts, and also as showing the tendency of the results 

 at which we have arrived. 



1. It may have been observed that in all those propositions 

 I have taken for granted the inflexion of the rays by the body 

 first acting upon them as well as their deflexion by that body, 

 and have reasoned on that supposition. It is, however, not 

 to be denied that we cannot easily perceive the fringes made 

 by the single inflexion, as we can without any difficulty 

 perceive those made by the single deflexion, and fully de- 

 scribed in Proposition I. Sir I. NEWTON even, assumes that 

 no fringes are made within the shadow. I here purposely 

 keep out of view the fringes made in the shadow of a hair or 

 other small body, because the principle of interference there 

 comes into play. However, I will now state the grounds of 

 my assuming inflexion and separation of the rays by their 

 different flexibility, when only a single body acts on them. 

 In the first place, the first body does act in some way ; for the 

 second only acts after the first, and if the first be removed the 

 fringes made in its shadow by the second at once vanish. 

 Secondly, these fringes made by the second depend upon its 

 proximity to the first. Thirdly, the following experiment 

 seems decisive. Place, instead of a straight edge, one of the 

 form in fig. 18, and then apply at some distance from it, the 

 second edge, as in the former experiments. You find that the 

 fringes assume the form, somewhat like a small-tooth comb, 



