MAGNETISATION ON THE THERMOELECTRIC QUALITY OF IRON. 
369 
determined in absolute measure by the same methods as those described in the paper 
referred to. To reduce the thermoelectric effects to absolute measure, the resistance 
of the circuit, consisting of the iron wire, leading wires, and galvanometer, was 
carefully determined, and the “ galvanometer constant ” was found by passing through 
it the current produced by exposing the ends of a coil of large and known resistance 
to a difference of potential amounting to rather less than yyy, (yot) °f the E.M.F. of 
a standard Daniell’s cell, the fractional potential being furnished in the manner 
sketched in fig. 11. From this was calculated the deflection which, in the actual 
thermoelectric circuit, would be produced by 1 microvolt (1 voltXlO -0 ), and the 
thermoelectric effects are expressed in microvolts. 
Fig. 11. 
§ 21. In all the following experiments pieces of iron wire from the same bundle 
were used, and the experiments of fig. 12 to fig. 31 inclusive were made with the 
same specimen. The wire was 0'61 mm. in diameter originally. After annealing it 
was stretched with a load of 12 kilos., which gave it a considerable permanent set, 
and reduced its diameter to 0'61 mm. The subsequent loadings were kept within 
this amount, and consequently caused no further permanent set. 
§ 22. In the first experiment, fig. 12, the wire had some residual magnetism, though 
no magnetising field was in action, in the direction of its length. The cycle of loads 
0 —11 kilos. — 0 was repeated several times, and the thermoelectric and magnetic 
effects were observed. In this case they have not been reduced to absolute measure ; 
and the scale readings are stated below as they were taken. The magnetometer and 
galvanometer readings are taken from the true zero. 
Load. 
Magnetometer. 
Galvanometer 
(thermoelectric 
current). 
Load. 
Magnetometer. 
Galvanometer 
(thermoelectric 
current). 
Ml 08. 
0 
37 
50 
kilos. 
11 
77 
-12 
2 
45 
69 
10 
78 
-23 
4 
70 
12 
8 
80 
-50 
6 
84 
-26 
6 
84 
-85 
8 
84 
-46 
4 
86 
-79 
10 
79 
-24 
2 
68 
-23 
11 
77 
-12 
1 
56 
+ 18 
0 
41 
50 
3 B 
MDCCCLXXXVI. 
