80 
MEASUREMENT OF HIGH TEMPERATURES. 
platinum-platinum, when these elements are regarded as the limiting 
cases into which any series of thermo-couples of platinum alloys must 
ultimately converge. A series of couples such as is here understood 
has already been defined. In each member of such a series pure plati- 
num is thermo-electrically combined with an alloy of platinum and a 
second metal, and the amount of the latter metallic ingredient decreases 
from alloy to- alloy of the series as far as zero. 
Having given a number of thermo-couples, A, B, (7, I) . . . , let the 
cold junction all be kept at the same constant temperature, t. In 
like manner let the hot junctions be exposed together to a second tem- 
perature, which, however, is made to vary continuously from a com- 
paratively low value to as high a value as may be admissible. Then 
will a comparison of corresponding values of electro- motive force indi- 
cate in how far the variation of the latter with temperature may be re- 
garded as uniformly continuous. Thermo-electric anomalies, such, for 
instance, as are presented by iron, nickel, probably by some platinum- 
iridium alloys, and by all metals at sufficiently high temperatures, are 
thus detected and located. In practice it is convenient to compare the 
thermo-couples in pairs; and like exposure of the hot junction is facili- 
tated by melting them to a common spherule with the oxyhydrogen 
blow-pipe. A tube may be placed in Fletcher's organic combustion- 
furnace or in an anthracite blast-furnace and the insulated thermo-ele- 
ments heated within it, with their common junction near the center of 
the tube. All wires so compared are supposed, of course, to be homo- 
geneous throughout their length. 
Table 8. — Equivalent thermo-electric powers. 
Pt, Pt If 
20%. 
No. 14. 
Pd, Pt Ir 
20%. 
No. 15. 
810 
1470 
1350 
2510 
4290 
8380 
4370 
8600 
4770 
9470 
5700 
11610 
6140 
12330 
7910 
16940 
7970 
17210 
8370 
18360 
T = 
850° 
Pt, Pt Ir 
20%. 
No. 14. 
810 
1350 
2250 
4280 
5690 
7018 
7680 
T = 
Pt, Pd. 
No. 13. 
1150 
1990 
4200 
5970 
7860 
8830 
S0Q° 
Pt, Pt Ir 
20%. 
No. 14. 
810 
1350 
2706 
3130 
4640 
6990 
7750 
Pt, Ni. 
No. 12. 
1830 
2990 
5120 
5590 
7000 
9450 
10210 
Pt, Pt Ir 
20%. 
No. 14. 
800'-' 
2900 
8430 
8470 
8570 
9030 
9550 
13190 
Pt.Ptlr 
5%. 
No. 19. 
1028 
2605 
2610 
2500 
2660 
2720 
3090 
At the end of this table the approximate value of the temperature 
reached in each of these comparisons is given. The values of electro- 
motive forces in this table (No. 14 being the couple common to all) 
show that the variations are practically uniform, so far as the compari- 
sons go. The table supplies an experimental test, which corresponds 
(734) 
