Translations:Analogy/45/en

Let us now summarize. According to Huygens, each point of a wavefront can be envisaged as a source of secondary spherical wavelets. Thus, one can determine the progress through space of a wavefront or of any portion of a wavefront. At any particular time, the shape of the wavefront is the envelope of all secondary wavelets. This technique, however, ignores most portions of each secondary wavelet, thus retaining only the portions that are common to the envelope. Because of this limitation, Huygens’ principle alone cannot account for the diffraction process - the prevalence of which is borne out by everyday experience. Sound waves easily bend around large objects such as telephone poles and trees which, on the other hand, cast fairly distinct shadows when illuminated by light. Yet Huygens’ principle is independent of any wavelength considerations and would predict the same wavefront behavior in both situations.