AND STRAIN ON THE ACTION OF PHYSICAL FORCES. 
163 
the 3 ohms were removed to be 58. In this way the following results were arrived 
at as the means of several trials :— 
Resistance in 
Position of 
Number 
the external circuit 
equilibrium of the 
proportional to 
of B.C. 
sliding-piece. 
the B.C. 
10 
56-7 
l’O 
3 
55-8 
2-8 
0 
557 
11-0 
Now when we bear in mind that one division of the iridio-platinum wire only 
represents an alteration of resistance of '0033 per cent., it appears evident that 
alteration of the strength of the B.C. can have but very small effect on the resistance, 
and even if there is any alteration it is of such a nature as to show that circular 
magnetization produces decrease, not increase of resistance. 
Discussion of Auerbach’s Experiments.* 
The results recorded in the last few experiments are so completely at variance with 
my own former observations,t and with those of Auerbach that it is very desirable to 
attempt to account for the discrepancies. I cannot help thinking that Auerbach 
experimenting, as it would seem, in almost precisely the same manner as I did in 
1875, may have been misled in the same way as I now believe myself to have been. 
We both employed copper terminals to our iron wires whose resistances were in some 
cases even greater than that of the wire itself, and therefore necessarily not very thick, 
and moreover balanced this compound wire of copper and iron against a wire of German- 
silver. Now when a current is passing through a wire compounded of two metals placed 
end to end, a “ Peltier effect ” is produced such that an electromotive force is developed 
which sends a current in the opposite direction to the original; so that, if we attempt 
to find the resistance of the compound wire in the usual manner by closing the battery 
circuit and shortly afterwards that of the galvanometer, we shall obtain an apparent 
value for the resistance which will depend upon the battery-power employed, upon the 
length of time that the battery circuit has been closed, upon the medium surrounding 
the wire,| and upon the thermo-electric power of the two metals forming the compound 
wire whose resistance we wish to determine. Nor is the “ Peltier effect ” necessarily 
confined to the two junctions, for since no wire can be made perfectly homogeneous 
* Phil. Mag., July, 1879. 
t Ibicl., June, 1875. 
+ That is whether this medium tends to preserve the inequality of temperature at the two junctions or not. 
Y 2 
