JEquipotmtial Lines of an Electric Current. 281 



effect to increase proportionally with the magnetic induction 

 through the metal.* 



As with the thin cross of cobalt, so with this thin cross of 

 nickel an endeavor was made to detect a permanent rotation of 

 the equipotential lines by a magnetic field of about 9000. No 

 such permanent effect was discovered. If any existed, it was 

 probably less than 1 per cent of the temporary effect. 



Crosses varying in shape of cross-section : Two crosses were 

 cut from a commercial cast-nickel electrode and worked to the 

 following dimensions approximately : 





Width of 



Thickness 



Length of 





Main part. Arms. 



between Arms. 



Main part. Arms. 



Ko. 1 . . 



grain 9mm 



l-32 mm 



931am ^mm 



Xo. 2.. 



... 0-5 - 0'5 



3-93 



20 6 



The comparison of these two crosses was very rough, as the 

 table here given will show. In this table M signifies, as usual, 

 the absolute intensity of the magnetizing field ; Tr. is the 

 transverse current, not in absolute measure, the direct current 

 being supposed constant throughout the whole series ; and P 

 is the R. P., not in absolute measure. 



p. 



104 

 160 



H 9 is} 1 * 



175 

 157 



107 



397 

 586 



It appears from this table, rough as it is, that in weak mag- 

 netizing fields the P. P. of No. 2 is about four times as great 

 as that of Tm 1, that as stronger and stronger fields are used 

 the R. P. of each diminishes, but that of No. 2 so much the 

 more rapidly that in a field of 8300 the two are nearly equal. 

 This accords well with the result of the somewhat similar tests 

 made with .Norway iron, and in this case, as in that, the differ- 

 ence in behavior of the two crosses appears to be entirely 



* For further evidence upon this point, on June 28, 1888, having- laid upon this 

 nickel cross a single loop of wire, I made tests similar to those described in my 

 article in this Journal last August as having been made with two crosses of iron. 

 The magnetizing forces used were about 5500 and 10000 respectively. The result 

 was approximately as follows : ratio of magnetic induction through the cross in 

 the two cases 1'8 ; ratio of transverse current in the two cases 1*1. 



Xo. 





Date. 





M. 



Tr. 



1. 



Sept. 



26, 



1887 



8300 



652 



u 



a 



a 



a 



5100 



616 



it 



a 



u 



a 



3450 ! 3330 

 3200 \ SS3 ° 



420 



u 



ec 



27, 



a 



457 



a 



a 



a 



tt 



2100 



279 



a 



a 



28, 



it 



1070 



127 



2. 



a 



26, 



it 



8300 



226 



u 



a 



a 



tt 



5100 



230 



u 



a 

 tt 



a 



27, 



tt 



3450 j 

 3200 i" 3330 



214 

 234 



a 



a 



i. 



a 



2100 



212 



it 



it 



28, 



tt 



1070 



160 



