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 sereen, as Newton and all the other 
experimenters had done hitherto ;—that they are found 
distinetly 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 
