Diffraction

Diffraction, in physical Optics, is that phenomenon exhibited by light-waves, of being deflected out of their rectilinear course when striking against the edges of obstacles. On account of the wave-lengths of light being extremely small, diffraction is not very pronounced; with waves of sound in air the analogous effects are much more marked, the sound-waves being much longer. Newton's great objection to the wave-theory of light was that light did not behave in the same way as other wave-motions, in travelling round corners, etc. Diffraction shows that it does behave in the same way, and that Newton's objection was therefore invalid. [Light, Wave-theory.]