barus.J METHODS OF PYROMETRY. 27 
Bock, ] Lion and Guichard 2 use iron and copper or iron and brass, either 
in the form of parallel rods or tubes bundled together or of a rod within 
a tube 5 in each case provided with a suitable index and dial arrange- 
ment. A like apparatus of metal and fire-clay (chamotte) is due to 
Bussius. 3 Finally, the use of graphite for pyrometry, an idea which 
long ago occurred to Daniell, was resuscitated by v. Steiule and Har- 
ting. 4 In their apparatus an iron tube surrounds a rod of graphite, and 
an ingenious mechanism permits only those parts which are actually 
exposed to the high temperature to act differentially on the dial. Ad- 
justment is made by means of mercury. Winkler, who first tested these 
apparatus, declared them serviceable, but his testimony is not corrobo- 
rated by Beckert. He finds that the indications of graphite pyrometers 
are neither strictly comparable nor very decisive, and that they are 
quite unreliable above 600°. This criticism applies to the pyrometers 
of the present class generally. 
Dilatation of liquids. — Pyrometers based on liquid expansion are few 
in number and quite unavailable. An old apparatus is described anony 
mously in Dingler's Journal 5 in which the expansion of a fused alloy in 
a porcelain bulb is registered by aid of a platinum rod moving along a 
scale. The division is in Wedgwood degrees. A similar apparatus 
was proposed by Achard. 6 Here the expansion of the alloy is to be 
read off directly in the translucent stem of the porcelain bulb. The 
construction, therefore, is that of the ordinary mercury thermometer. I 
doubt whether either of these instruments has ever been used. Person 7 
applied a new principle. He found that mercury under 4 atmospheres 
pressure boils above 450°, under 30 atmospheres pressure above 500°; 
that the dilatation in these cases is quite notable. Here I may refer to 
experiments of Bystrom, 8 to whom a hydro- pyrometer is due, and to 
Waterston, 9 by whom the expansion of w r ater at high temperatures 
(300°) under pressure has been specially investigated. Waterston 
formulates his data and is led to the striding result that water at 300° 
expands at a greater rate than " permanent gases. Water at high 
temperatures and pressures attacks glass, rendering it opaque and 
thus putting an end to the experiment. 
Dilatation of gases (manometric methods). — According to Shaw 10 a 
rudimentary air thermometer was built by Amonton in Paris about as 
1 Bock: Ibid,, vol. 195, 1870, p. 312. 
2 Lion et Guichard : Ibid., vol. 220, 1876, p. 37. 
3 Bussius : Ibid., vol. 164, 1862, p. 107. Berg- und Hiittenm. Zeitung, No. 10, 1862. 
4 v. Steinle and Harting : Clemens Winkler's report in Zeitschr. fur Analyt. Chem., 
vol. 19, 1880, p. 63; Beckert's report in ibid., vol. 21, 1882, p. 248. 
6 Dingler's Jour., vol. 32, 1829, p. 355. 
e See Becquerel: Ann. ch., 3d series, vol.78, 1863, p. 52. 
7 Person : Comptes Rendus, vol. 19, 1844. p. 757. 
8 Bystrom : Berl. Ber., 1862, p. 344. 
* Waterston : Philos. Mag., Lond., 4th series, vol. 26, 1863, p. 116. 
I0 Enc. Brit., vol. 20, 1886, p. 129. 
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