DI'ATHER'MANCY (from out, ilia, through elp/Aa Pats, Mt rnionsis„ It heating, inn]] Oep I.LaiPeo•• t'irminein. to heat, from Oeppos, ON. warm: Connected with Lat. f ornms, Skt. gharnor, hot ). A term used to express that qual ity of a body in virtue of which those ether e at are allowed to pass which produce thermal effects to a marked degree; it may. in general language. be (-ailed lranspareney to heat.' .1I1 ether-waves energy: and in many eases when these wave: are absorbed their energy is spent in producing heat effects. (ills is not so, of course, when the energy of the waves goes to abculeaI or eleetrical :lethal.) It is found that in the trim, of ether-waves emitted by any body. s.g. the sun. the energy carried by watt's of different WaVe•Iiiiiillier is in general ibith.rent ; similarly. the transparency of a body to ether waves tanks with their wave-number. In diA elissing diallierinalley. therefore. it is necessary to consider both the total radiation transmitted and al-o the wave numbers of these waves. (So!
1:.‘otATioN.) In general terms, the greater por tion of the energy carried from the sun and from other bodies by etlier-waves is associated with waves Whose wave-numbers are so small that they do affect our sense of sight ; and other tiSteima tits have to be used to detect the and measure their energy. Such are I hermometers, radiomierom•ters, radiometers. etc. it i- possible to bodies which are absolutely opaque to those waves which affect our eyeR, and set are Iralisparelit to naves which have a les: wave-number: and the converse is true. The diathernaincv of a body depends upon its tem perature and upon its thickness. For a most in terest de-eription of the transparency of bodies of all kinds to heal, reference should be wade to Tyndall, !feat as a Mode of Motion (tali ed., London, 18:s0).