Equipotentiai Lines of an Electric Current. 433 
Date. Temp. M. CO. Rie. 
1884, July 26th. 218 1696 1150) | +114100x 10-19 
Aug. 8th. 21:1 1638 "1104 | +117300 
Aug. 8th. 3 1638 1104 | +123900 
99 
29 
The two trials of August 8th were not entirely independent 
of each other, as only one test of the intensity of the magnetic 
field and of the sensitiveness of the Thomson galvanometer 
was made during the two trials of that date. The results as 
they stand indicate an increase of the rotational power with 
fall of temperature ; but the experiments were two hasty to 
justify a conclusion upon the matter. 
Several experiments have resulted from the criticisms or 
suggestions of other investigators. 
Mr. Bidwell’s Theory. 
This has been so recently and so widely published that it is 
hardly necessary for me to state it in detail. 
In ‘ Science’? (March 28th, 1884) I replied very briefly to 
Mr. Bidwell’s first paper, stating that I found the transverse 
current in a strip of soft steel to be in the same direction 
when the strip was fastened to the supporting plate by a clamp 
across the middle of the strip only, as when it was fastened by 
means of clamps at its ends only. 
Mr. Bidwell has, in his second paper (Phil. Mag. April 
1884), described an experiment which he appears to consider 
conclusive against the previously accepted view of the “ rota- 
tional effect.”” In brief he obtains what he calls a “ reversal”’ 
of the transverse effect in gold, using a strip of that metal 
haying two narrow longitudinal slits lying on the same straight 
line and nearly meeting in the centre of the strip. 
IT shall not undertake here an extended discussion of this 
interesting experiment of Mr. Bidwell. My view of the matter 
is in substance as follows :— 
Let J in fig. 3 represent an equipotential line in a strip of 
metal through which an electric current is flowing, the metal 
being in a normal condition. 
In fig. 4 J represents the corresponding equipotential line 
when the metal strip is acted upon by a powerful magnetic 
force in a direction perpendicular to the plane of the paper. 
If, now, a and b be connected by means of a wire, a current 
will flow from a to b through the wire. If a’ and 0’ be con- 
