Equipotential Lines of an Electric Current. 435 
indicated that the rotational effect in nickel should be greater 
at low than at high temperatures. He therefore called in 
question the conclusion to the contrary which I had drawn 
from certain hasty and very rough experiments made before 
the use of the water-tank gave me the means of easily con- 
trolling the temperature of the metal under examination. I 
have therefore recently taken up the matter again. I used 
the same piece of nickel with which the former test was made 
(Phil. Mag. Sept. 1881, p. 163); but the strip was now so 
much damaged while being fastened upon glass, that it was 
necessary to cut its width down a good deal in order to obtain 
the “arms”’ for the side connections. The following Table 
shows the results obtained :— 
No. of Exp. Date. Temp. M. C. digpli Be 
f. July 28,1884.) 22 1717 | :08074 | 14940x10-% 
2. » 28 49 | 1703 | :03135 13760 ,, 
3. ys) 20°5 1652 | ‘03140 Lay LO ses 
4, 5» oO 2°2 1636 | 03123 T2810" 5; 
5. fie 21-2.) 1629 | -03121 15060 __,, 
6. Aug. 1 2°8 1671 | :03137 13180 
7. ye. 26°1 1691 | 03140 | 15110 ,, 
8. Ls ae 4-1 1627 | 03112 13220 _,, 
Combining the Ist, 3rd, 5th, and 7th, we have 
Temp. RiP. 
22°°5 TAICOS 10: 
From the 2nd, 4th, 6th, and 8th we have 
3°°5. 13240 x 10-°. 
Decrease for 1° fall of temperature = approximately ‘6 per 
cent. | 
It will be noticed that the results obtained at low tempe- 
ratures do not accord so well as those at high temperatures. - 
This fact is in all probability due to the difficulty experienced 
in preventing slight fluctuations of temperature while the 
colder water was flowing through the tank. Irregularity in 
the flow of this water causes disturbing thermo-electric 
currents. 
The quantity called R. P. in this paper corresponds to the 
; 
= of my 1881 paper divided by the F. of that paper. Cal- 
culating the R. P. of nickel from the 188 experiments, I find 
it to be about 12700x10~”, for a field of intensity 1660. 
