26 MEASUREMENT OF HIGH TEMPERATURES. 
reliable because of the tendency of clay to shrink irregularly and to 
warp, and because of its dependence on the kind of clay used and on 
the time of exposure. After this the use of single-solid pyrometers 
seems to have been abandoned until quite recently, when Mr. Nichols, 1 
in comparing the resistance-temperature formulas of Beuoit, Siemens, and 
Matthiesseu with his own, found the linear dilatation of platinum very 
serviceable for the co-ordination of his data. He gives preference to 
the expansion thermometer over the resistance thermometer whenever 
the special constants of both instruments are unknown. 
The absence of further devices for single-solid pyrometry is not re- 
markable when the vast numbers of pyrometers in which solids are com- 
bined differentially are taken into view. Some of the earliest attempts 
of this kind are due to Borda, 2 although Guyton-Morveau (loc. cit.) was 
probably the first observer who had pyrometric ends in view, the solids 
adopted being platinum and porcelain. This physicist was at some 
pains in systematizing the dilatation of solids. More elaborate attempts 
to utilize the occurrence of different expansibility in solids for pyro- 
metric purposes are due to Daniell. 3 DanielPs substances are platinum 
and black lead, with a suitable interposition of clay, and his work on 
the dilatation of solids is elaborate, but unfortunately without much 
permanent value. • 
Following Daniell come a host of inventors whose apparatus, though 
often exceedingly ingenious, have only technical importance. These 
may therefore be passed over with a single brief mention here. Peter- 
sen 4 has a platinum wire in an iron tube ; Gibbon 5 exposes rods of iron 
or steel, and copper provided with a contact lever; Oechsle 6 utilizes an 
iron-brass spiral working on the principle of Br^guet's metallic ther- 
mometer, while Clement 7 replaces the metals of such a spiral by plati- 
num and silver. Priusep, 8 however, held that even this apparatus is 
not reliable on account of the tendency of the metals to alloy — a con- 
clusion which has WeinholdV assent. Gauntlet, 10 Desbordes, 11 Oechsle, 12 
'E. L. Nichols: Am. Jour. Sci., 3d series, vol. 22, 1881, p. 363. 
2 Borda: Boit Traite, I, 1816, p. 159. The use of iron and brass seeins first to have 
been made by Felter in Braunschweig. 
3 Daniell : Experiments with a new register pyrometer for measuring the expansion 
of solids; Jour. Royal Soc, London, vol. 11, p. 309; Philos. Mag., London, 2d series, 
vol. 10, 1831, pp. 191, 268, 297, 350; ibid., 3d series, vol. 1, 1832, pp. 197,261; Din- 
gler's Jour., vol. 19, p. 416; vol.43, p. 189; vol. 46, pp. 174,241. 
4 Petersen : Gehler. Phys. Worterb., 2d series, vol. 7, p. 994. 
5 Gibbon: Dingler's Jour., vol. 68, 183-<, p. 436. 
6 Oechsle: Ibid., vol. 60, 1836, p. 191. 
7 Clement: Ibid., vol. 80, 1843, p. 241. 
s Prinsep: Ibid., vol. 28, 1828, p. 421. 
'■' Weinhold: Dingler's Jour., vol. 208, 1873, p. 125. 
10 Gauntlet: Ibid., vol. 157, 1860, p. 279. 
11 Desbordes: Ibid., vol. 157, 1860, p. 279. 
12 Oechsle: Ibid., vol. 160, 1:861, p. 112; ibid., vol.196, 1870, p. 218. 
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