interference

(in-tér-fér’ens), n. [= F. inter- Sérence = Pg. in terfe ren cia = It. interferenza; as interfere + -ence.] 1. The act of interfering; interposition; especially, intermeddling. This circumstance, which is urged against the bill, becomes an additional motive for our interference. Burke; On Fox’s East India Bill, A part of the European powers have attempted to establish a right of interference to put down revolutionary principles in that continent. Woolsey, Introd. to Inter. Law, § 45. 2. A clashing or collision; the act of coming into violent contact.—3. In farriery, a striking of one foot against the one next to it, as one hind foot against the other.—4. In Amer. patent law, the conflict between two patents or applications for patent which claim in whole or in part the same invention. Henee, to go into interference (of an application for a patent) is to be reserved for the purpose of litigating the question in the patent office before the application shall be granted. 5. In physics, the mutual action of waves of any kind (whether those in water, or sound-, heat-, or light-waves) upon one another, by which, under certain conditions, the vibrations and their effects are increased, diminished, or neutralized. ‘The term was first employed by Dr. Young to exve pre certain phenomena which result from the mutual action of the rays of light on one another. In general, if two systems of waves come together, they interfere —that, is, they unite to reinforce or destroy one another, the actual disturbance of the medium at any instant being the resultant of the two disturbances considered separately. For example, if the two systems are of equal intensity and ] in the same phase, the result will be a doubled disturbance; if, however, they are half a wave-length apart, the result will berest. Thus, two sounds of the same pitch and intensity produce a note of double the intensity when they 1 meet in the same phase, the point of condensation of one corresponding to that of the other; when, on the other hand, the point of maximum condensation of the first corresponds to that of rarefaction of the other, they destroy each other. Again, if two notes differing but slightly in pitch (say one vibration per second) are sounded together, there will be one instant in each second when the two wave-systems will nearly coincide in phase, and one when they will be half a wave-length apart; the result is that they alternately strengthen and weaken each other at these moments, and the ear perceives the pulsations in the note called beats (see beatl, 7). The same principles hold true in the case of light, as was first shown by Young. The interference of light-waves is illustrated by the phenomena of diffraction (see diffraction): thus, a diffraction grating gives with monochromatic light a series of light and dark bands (interference fringes), corresponding respectively to the points of maximum and minimum motion resulting from the mutual action of the two wave-systems; for the former they are in the same phase, for the latter they differ in phase by half a wave-length. If white light is employed, a series of spectra (interference specti'a) of different orders is obtained. Newton’s rings, obtained, for example, when ordinary light is reflected from a convex lens of long focus pre ed upon a plate of gla , are circular interference spectra. The colors of thin films, as of oil on water or of a soap-bubble, are due to interference, as is also the iridescence of some antique gla or of mother- Interference Figure of a of-pearl, Still again, the beaut i- Uniaxial Crystal. ful figures produced when a sec- 198 3143 tion of a uniaxial crystal cut normal to the axis, or of a biaxial crystal cut normal to the bisectrix, is viewed in converging polarized light are similar phenomena, and are hence called interference figures. Recently (1888-9) Hertz Interference Figures of a Biaxial Crystal: (x) when the axial plane (pa ing through the two ovals) is inclined 45° to the vibration-planes of the polarizer and analyzer, and (2) when it is respectively parallel and perpendicular to them. has shown that electric waves, produced, for example, by induction discharges between two metal surfaces and propagated through space. also exhibit under proper conditions interference phenomena. These waves may have alength of several feet. See wave.=Syn, 1. Mediation, Intervention, etc. See interposition. interferer (in-tér-fér’ér), ». One who or that which interferes.