babus] METHODS OF PYROMETRY. 49 
facility of manipulation as is compatible with the character of the ex- 
periment. My object has been to place the calibration problem within 
the reach of the laboratory uot specially equipped for high temperature 
work, and though I have worked independently, I am glad to defer the 
priority of principle to Schinz. In addition to his air thermometer 
Schinz invented a torsion galvanometer on the principle of Coulomb's 
torsion balance, for the measurement of thermo currents. This instru- 
ment also does credit to his experimental sagacity. His couple is 
iron-platinum, having failed to obtain reliable data with Becquerel's 
platinum-palladium couple. Schinz does not give any absolute data, 
and it is easily seen that the absolute value of results with his bulb 
could not lay claim to accuracy. He fails, for instance, to discern the 
iron anomalies of which Tait 1 subsequently made considerable study. 
Tait's memoir is well known. Following the suggestion of Thomson, 2 
Tait makes an elaborate survey of the diagram by which the thermo- 
electrics of metals generally are to be expressed. For the measure- 
ment of temperature Tait uses a thermo-couple of platinum and plati- 
num-iridium alloy, and, so far as I have been able to find, his researches 
are the first in which the pyrometric use of the platinum iridium alloy 
is recorded. I may add here that special attention to the platinum- 
iridium alloys seems first to have been given by Deville and Debray, 3 
to whom we owe so much of the metallurgy of the platinum group. 
A special study of the thermo electrics of platinum-iridium and other 
alloys is due to Knott and MacGregor. 4 Diagrams are investigated for 
these alloys, applying between 45° and 400°, and for compositions as 
high as 20 per cent, of iridium. They also study silver palladium, iron- 
gold, and pi atinum- silver alloys with the same ends in view. In a 
late research Knott, MacGregor, and Smith 5 determine the thermo- 
electrics of cobalt. Having studied the platinum-iridium alloy calori- 
metrically, Le Chatelier 6 suggests the occurrence of an allotropic modi- 
fication of the alloy above red heat, the behavior being the same as that 
shown by iron at about 700°, and between the melting points of silver 
and gold. Furthermore, with the object of checking the formulas of 
Avenarius 7 and Tait, 8 Le Chatelier 9 avails himself of the fusing points 
of Violle. It appears that these formulas apply up to a certain tempera- 
ture, above which ( u brusquement") a second formula with new constants 
is applicable. Platinum, platinum alloys of iridium, copper and rho- 
1 Tait : Trans. Royal Soc. Edinburgh, vol. 27, 1872-73, p. 125. 
2 Thomson: Philos. Trans., London, vol. 14G, 1856, p. 649. 
3 Deville et Debray: C. R., vol. 81, 1875, p. 839; Cf. Ann. ch. et phys., 3d series, vol. 
56, 1859, pp. 431 (indium), 415 (rhodium). 
4 Knott and MacGregor: Trans. Royal Soc. Edinburgh, vol. 28, 1876-77, p. 321. 
5 K., M., andS. : Proc. Royal Soc. Edinburgh, vol. 9, 1876-77, p. 421. 
6 Le Chatelier: Bull. Soc. chimique, Paris, vol. 45, 1886, p. 482. 
7 Avenarius: Pogg. Ann., vol. 119, 1863, p. 406; Ibid., vol. 149, 1873, p. 372. 
«Tait: Trans. Royal Soc. Edinburgh, vol. 27, 1872-73, p. 125. 
*Le Chatelier; C. R., vol, 102, 1886, p. 819. 
Bull. 54—4: (703) 
