DIFFRACTION. 247 



tion ; he thought he saw here the manifest proofs of an 

 intense attractive and repulsive action, which bodies 

 exercise on rays passing close to them. This action, 

 supposing it real, could only be explained by admitting 

 the materiality of light. The phenomena of diffraction, 

 then, deserves in an eminent degree to fix the attention 

 of physicists. Many in fact studied it, but by very 

 inexact methods ; Fresnel finally gave to this class of 

 observations a perfection unhoped for, in showing that 

 in order to see these diffracted bands, it is not necessary 

 to receive them on a screen, as Newton and all the other 

 experimenters had done hitherto ; that they are found 

 distinctly in space, where we can follow them with all 

 the resources which result from the employment of the 

 astronomical micrometer, with a high magnifying power. 



According to the precise observations of Fresnel, by 

 the aid of these new modes of observation, if we still 

 wish to attribute the effects of diffraction to attractive or 

 repulsive forces acting on material elements, we must 

 admit that these actions are totally independent of the 

 nature or density of the bodies employed, for a spider's 

 thread and a wire of platinum produce bands exactly 

 the same ; the masses have no more influence, since the 

 back and the edge of a razor produce the same effect. 

 We find ourselves inevitably brought to this conclusion, 

 that a body acts on the rays passing near its surface with 

 so much the less energy as the rays come from a greater 

 distance, since, if on placing the luminous point at the 

 distance of a centimetre, the angular deviation is 12, it 

 will not amount quite to 4 in similar circumstances with 

 light coming from ten times the distance. 



These various results, especially the last, are impos- 

 sible to reconcile with any idea of an attraction. The 



