THE NERNST GLOWER. 83 



belongs to the same class of radiators as platinum and a "black body," 

 they computed 4^=2450 abs., and >} min =22oo abs. 



Their computed energy curve of a "black body" having its maximum 

 emission at 1.2 a departs considerably from the observed curve. Men- 

 denhall and Ingcrsoll compared the emission of the Nernst glower in terms 

 of a constant comparison lamp, at a certain wave-length in the visible 

 spectrum, at the melting points of gold and of platinum. From this they 

 extrapolated on a straight line assuming that Wien's equation holds for 

 the glower, and found the temperature at normal or any desired power 

 consumption. This leads to erroneous values (which are probably too 

 high, as will be shown presently), due to the fact that the spectrum is the 

 composite of numerous emission bands, which rapidly increase in intensity, 

 in the short wave-lengths, with rise in temperature. They found the 

 normal temperature to be 2300 abs., disagreeing with a recent determina- 

 tion by Hartman, 1 who, by means of thermocouples of different thickness 

 placed against the glower, correcting for heat conduction by extrapolating 

 to a temperature corresponding to an infinitely thin couple, found the 

 temperature to be 1800 abs. Although this method had previously been 

 extensively used, with fair success, in measuring temperature of gas- 

 flames, it is not suited to the glower, in which there is no layer of hot gas 

 to even partially compensate for the heat lost by conduction. 



That the Nernst glower emits selectively in the visible spectrum, has 

 been shown by Kurlbaum and Schulze, 2 who found a minimum of emission 

 at 0.52 n, which became fainter with rise in temperature, and disappeared 

 entirely at high temperatures. 



To this brief review of what has been done on the Nernst glower may 

 be added a paper by its inventor, 3 who showed that the conductivity is 

 electrolytic, while Kaufmann 4 showed that in spite of the entirely different 

 inner mechanism of conduction of a gas in a vacuum-tube, and in a Nernst 

 glower, the electrodynamic phenomena are nevertheless very similar. 



The present investigation of the Nernst glower consists in mapping 

 the distribution of energy in the spectrum, varying the power consumption, 

 and hence the temperature. 



The apparatus used in this work consisted of the mirror spectrometer, 5 

 used in the preceding experiments, a perfectly clear fluorite prism, having 

 an angle of 6o and circular faces ^ mm. in diameter, and a bolometer 8 

 with a hemispherical reflecting mirror. The bolometer strip and spectrom- 

 eter slit were 0.6 mm. wide, or about 4' of arc. The upper part of the 



1 Hartman: Phys. Rev., 17, p. 65, 1903. 



2 Kurlbaum & Schulze: Verh. Phys. Gesell., 5, p. 428, 1903. 



3 Nernst: Zeit. fur Electrochemie. 6, p. 41, 1899. 



4 Kaufmann: Ann. der Phys. (4), 2, p. 158, 1900; 5, p. 757, 1901. 



5 For adjustments see "Investigations of Infra-red Spectra," Carnegie Institution of 

 Washington Publication No. 35, 1905. 



6 Described in this volume, Appendix II. 



