The encyclopædia britannica; a dictionary of arts, sciences, literature and general information . rlbaum (Ann. Phys., 1901, 4,p. 649) extended the residual reflection method to a temperaturerange from —190° to 1500° C, and employed the rays reflected from quartz 8S>i, and rocksalt 51 p, inaddition to thosefrom fluorite. It ap-peared from theseresearches that therays of great wave-length from a sourceat a high temperaturetended to vary in thelimit directly as theabsolute temperature of the source, as *? •Mi»o«.,,,i,:„i, „/j .-„,.i,i spectrum of full radiation at 2000° , and could
The encyclopædia britannica; a dictionary of arts, sciences, literature and general information . rlbaum (Ann. Phys., 1901, 4,p. 649) extended the residual reflection method to a temperaturerange from —190° to 1500° C, and employed the rays reflected from quartz 8S>i, and rocksalt 51 p, inaddition to thosefrom fluorite. It ap-peared from theseresearches that therays of great wave-length from a sourceat a high temperaturetended to vary in thelimit directly as theabsolute temperature of the source, as *? •Mi»o«.,,,i,:„i, „/j .-„,.i,i spectrum of full radiation at 2000° , and could ^ccording to formulae of Planck & be represented by Wiens formula with any value of the constant c. Thesimplest type of formula satisfying the required conditionsis that proposed by Max Planck (Ann. Phys., 1901, 4, p. SS3)namely, E = C\-«(e7*»-i) «, which agrees with Wiens formula when 0 is small, where Wiensformula is known to be satisfactory, but approaches the limiting. HEATH, B.—HEATH, N. 5 / HJtMCJT JMrm / k / / / 1*1 f IN »• j«b FiC. 9.—Variation ofenergy of radiation cor-responding to wave-length 30 ii, with tem-perature of source. form E = CX~V/c, wlienO is large, thus satisfying the conditionproposed by Lord Rayleigh. The theoretical inlcrpretalion ofthis formula remains to some extent a matter of future investiga-tion, but it appears to satisfy experiment witliin the limits ofobservational error. In order to compare Plancks formulagraphically with Wiens, the distribution curves correspondingto both formulae are plotted in fig. 8 for a temperature of 2000°abs., taking the value of the constantc= 14,600 with a scale of wave-lengthin microns ju. The curves in fig. 9illustrate the difference between thetwo formulae for the variation of theintensity of radiation corresponding toa fixed wave-length 30 fx. AssumingWiens displacement law, the curvesmay be applied to find the energy forany other wave-length or temperature,by simply alterin
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