On the Thermoelectric Position of Platinoid, 163 



spectra, but account must be taken of dispersion (see further 

 on). 



16. For the experimental determination of the two co- 

 efficients of emission in the visible spectrum measured in 

 calorimetric measure, we must determine for a definite 

 body, best a perfectly black one, the radiation in calorimetric 

 measure, and compare (by the method to be explained im- 

 mediately) with its brightness that of the body to be investi- 

 gated, by making the brightness of the two bodies exactly the 

 same, since with equal brightness the energies of the rays per- 

 ceived by the eye in the same regions of the spectrum are 

 equal. We thus fix the ratio of the energies received by the 

 apparatus ; these are themselves proportional to the coefficients 

 of emission of the two sources of light, and are further 

 dependent upon the distance of the luminous body, the thick- 

 ness of the radiating layer, &c. (see further on). Further, 

 the dispersion must be taken account of. 

 [To be continued.] 



XXV. Note on the Thermoelectric Position of Platinoid. By 

 J. T. Bottomley, M.A., F.R.S., F.C.S., and A. Tana- 

 k ad ate, Rigahusi*. 



IN carrying out a series of experiments on radiation of heat 

 by solid bodies, an investigation to which one of the pre- 

 sent writers has for some time past devoted considerable atten- 

 tion, it became necessary, for a purpose which need not here 

 be detailed, to select a thermoelectric pair of metals, of which 

 one metal was essentially platinum, as it had to pass through 

 glass. Various pairs were considered, and some trials were 

 made ; and it was finally determined to make use of platinum 

 and platinoid. The latter metal is an alloy whose electrical 

 and mechanical properties were investigated some years ago 

 by one of the present writers f; and since that time it has 

 assumed considerable importance in the construction of elec- 

 trical instruments and resistance-coils. Partly on this account, 

 and partly from present requirements, it became both inter- 

 esting and necessary to determine the thermoelectric constants 

 for a specimen of this alloy. 



Platinoid is in composition very similar to German silver. 

 In the manufacture of the alloy, however, phosphide of tung- 

 sten is employed; and although an exceedingly minute 



* Reprinted at the request of the Authors, having been read before the 

 Royal Society, June 20, 1889. 



t J. T. Bottomley, Roy. Soc. Proc. 1885. 



