44 MEASUREMENT OF HIGH TEMPERATURES. 
opaque bodies by Becquerel, 1 involved him in a dispute with dela Pro- 
vostaye 2 in which, however, the position of the former was not seriously 
impugned. 
Decharme, repeating Pouillet's experiments, concludes that the inten- 
sity of the glow of metals, particularly of platinum, is largely dependent 
on the thickness of the wire. After this Crova 3 undertook a long series 
of experiments, in the course of which he made the subject of radiation 
pyrometry 4 practically his own. The law of emission being known, 
temperature may at once be measured spectro-photometrically. Crova 
in some of his experiments obtains his radiation directly from the bulb 
Of a porcelain air thermometer. His results confirm BecquerePs datum 
that the emissive power of absolutely* opaque bodies is the same. A 
series of experiments on radiation and temperature was published by 
Nichols, 5 who also uses his own results for a critical discussion of the 
work of Crova (1. c.) and of the indications of the radiation pyrometer 
in general. In the same year Stefan 6 published his law of radiation, 
according to which the amount of heat emitted by a hot body in vacuo 
increases as the fourth power of its absolute temperature. Violle, 7 
using Gray's and Trannin's photometer, determined the photometric 
intensity of light emitted by glowing platinum at different tempera- 
tures, results which he endeavors to formulate. Similar experiments 
he subsequently makes for silver nearly at its melting point. An ex- 
periment with reference to temperature aud incandescence was pub- 
lished by Bezold. 8 To put the law proposed by Stefan (1. c.) to a prac- 
tical test, Schneebeli 9 commenced a series of experiments in which ther- 
mal measurements between 400° and 1,200° were made by a porcelain 
airthermometerof Schneebeli's 10 own construction. Eadiation measure- 
ments are made by a crude bolometer n of tin foil, the instrument which 
Langiey 12 has carried to a remarkable degree of perfection. Schnee- 
1 Becquerel : C. R., vol. 57, 1863, p. 681; Anualeschiinie, 4th series, vol. 1, 1864, p. 120. 
2 Do la Provostaye: C. R. vol. 57, 1863, p. 637 ; Ibid., p. 1022. The older papers of 
de la Provostaye et Dessains; see Aun. de ch. et phys., 3d series, vol. 12, 1844 ? p. 129; 
Ibid., vol. 16, 1846, p. 337; ibid., vol. 22, 1848, p. 358; also de la Provostaye : Ibid., 
vol. 67, 1863, p. 1. Dulong and Petit's older radiation work is given in Ann. ch., 2d 
series, vol. 7, 1817, pp. 113, 225. 
3 Crova: C. R., vol. 87,1878, pp. 322,979; C. R., vol. 90, 1880, p. 252 ; Ann.chhn. et 
•phys., 5th series, vol. 19, 1880* p. 472 ; Jour, de phys., vol. 8, 1879, p. 196. 
4 Regarding spectrophometric work upon which measurement like the present 
largely depends, see Govi : C.R., vol. 50, 1860, p. 156; Trannin, Jour.de phys., 
Paris, vol. 5, 1876, p. 297 ; Vierordt: Pogg. Ann., vol. 1, 37, 1869, p. 200; Glan : Wied. 
Ann., vol. 1, 1877, p. 351. 
5 Nichols: Am. Jour. Sci., 3d series, vol. 18, 1879, p. 446; ibid., vol. 19, 1880, p. 42. 
fi Stefan : Wien. Ber., vol. 79, 2d series, 1879, p. 391. 
7 Violle : C. R., vol. 92, 1881,'p. 866, 1204 ; C. R., vol. 96, 1883, p. 1033. 
8 Bezold: Wied. Ann., vol. 21, 1884, p. 175. 
9 Schneebeli: Wied. Ann., vol. 22, 1884, p. 430. 
10 Schneebeli: Arch, sci., phys. etnat., Geneva, vol.8, 1882, p. 244. 
u Svanberg: Pogg. Ann., vol.84, 1851, p. 411. 
12 Langiey: Am. Jour., 3d ser., vol. 21, 1881. p. 187. 
(698) 
