50 MEASUREMENT OF HIGH TEMPERATURES. 
dium, ami palladium are tested, and he finds that high temperature 
measurements thermo electrically made can be relied upon to 20°. "II 
resulte de mes recherches," adds he, <: quela loi d'Avenarius et Tait 
continue a se verifier au-dessus de 400° avec une approximation egale 
a celle qu'elle comporte au dessous, jusq'a une certaine temperature 
limite, variable avec la nature des couples consideres." The superior- 
ity of the platinum-rhodium couple 1 of Le Chatelier's (which is his special 
contribution to thermo-electric pyrometry) over the iron platinum or 
platin-palladinm couples is due to greater homogeneity of the former, 
and the fusing point calibration may be considered accurate within 5° 
C. In a very full paper recently published, Le Chatelier 2 shows that 
the condemnation which was inflicted on Pouillet and BecquereFs 
methods was thoroughly unjust. Believing the fusing and. boiling 
point method of calibration to be superior to direct comparison with the 
air thermometer, he selects the series, H 2 (100°), Pb (323°), Hg (358°), 
Zn (415°), S (448°), Se (665°) Ag (945°), Au (1045°), Ou (1054°), Pd 
(1500°), Pt (1775°), most of which values are due to Violle (1. a). 
Having, moreover, given attention to the errors due to homogeneity Le 
Chatelier concludes with Becquerel, 3 and many others 4 before him, that 
to make the Avenarius-Tait formula sufficiently applicable it is neces- 
sary either to add a cubical term or else to use two laws, one for low and 
the other for high temperatures. In a final memoir Le Chatelier 5 invents 
an ingenious method for fusing point measurement, and compares his 
results with those of Carnelley (1. c). The table given contains data for 
alkaline and metallic chlorides, cast-irons, nickle, etc., and the paper 
ends with an investigation of the temperature of chemical phenomena 
in which heat is absorbed or disengaged, or in which the substances 
undergo transformation. 
Finally, I desire to add that the thermo electric effect of changes of 
physical state and of molecular changes in general, has not been left 
unnoticed. Obermayer's 6 experiments largely refer to alloys which 
melt at comparatively low temperatures. Tidblom 7 investigates an 
amplified form of the thermo- electric equation, in which changes of the 
kind in question may be allowed for. 
Electrical conductivity. — The measurement of temperature in terms 
of electrical conductivity was not attempted at so early a date as the 
thermo-electric methods. Mliller 8 attempted to co-ordinate tempera- 
ture and resistance both for iron and for platinum, without, however, 
more than estimating the thermal datum. A resistance thermometer, 
1 Lo Chatelier: Bull. Soc. chimique, Paris, n. s., vol. 47, 1837, p. 2. 
2 Le Chatelier: Jour, de physique, vol. 6, 1887, p. 23. 
3 Becquerel: Aim. ch. et phys., Paris, 3d series, vol. 68, 1863, p. 49. 
4 Cf. Moussou : Physik, Zurich, 2d ed., vol. 3, 1874, p. 384. 
r, Lo Chatelier: Bull. Soc. chimique, Paris, n. s., vol. 47, 1887, p. 300. 
^Obermayer: Wien. Ber., vol. 66, pt. 2, 1872, p. 63. 
'Tidblom : Beibl., vol. 1, 1877, p. 151. 
8 MUUor : Pogg. Ami., vol. 103, 1858, p. 176 
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