Equipotential Lines of an Electric Current. 137 



R. P. is smallest in ]STo. 5, larger in No. 7, still larger in No. 

 6, and largest in No. 8.* 



In the test already described the P. P. of No. 8 was, in fact, 

 three times as great as that of No. 5, and as the latter was 

 quite strongly magnetized, it seemed not unlikely that No. 8 

 was in a condition approaching what is called the state of 

 magnetic saturation. If this were the case, No. 8 probably 

 would, when placed in a stronger magnetic field than that used 

 Dec. 31st, suffer a diminution of its P. P., while Nos. 5, 6 and 

 7 should show less or no diminution of this sort under similar 

 circumstances. Accordingly on Jan. 1st, 4*8 cells, 6 abreast, 

 were used in the magnet circuit, the number used the day 

 before having been 30, 6 abreast. This brought the magnetic 

 field up to about 7000. ' The four crosses were then tested 

 essentially as on Dec. 21st, the order being as before, Nos. 7, 

 8, 6, 5, 5, 6, 8, 7. The numbers given by this trial, like those 

 obtained Dec. 31st, are only comparative. They do not repre- 

 sent the absolute values of the P. P's, and for convenience 

 they have been reduced to such a scale as to give No. 5 the 

 same representative number that it had in the results of 

 Dec. 31st. 



Results of Jan. 1st, 1886, with magnetic field about 7100 

 (c. g. s.) :— 



No. 5 10 9 l I 



R. P. on arbitrary scale. Mean. 



f 

 f 



! 



152 

 154 

 144 



148 

 260 

 270 



153 

 146 



265 



On comparing these figures with those given above, it 

 appears that the relative standing of Nos. 5, 6 and 7 was 

 affected very slightly, by going from the weaker to the stronger 

 magnetic field, but No. 8 shows a great falling off. So great, 

 in fact, was this charge in No. 8, that the observations made 

 at this time did not clearly show whether the magnetic field of 

 about 7100 produced upon the equipotential lines of the elec- 

 tric current in this cross .an effect greater or less than that 

 produced by a field of less than 6000. But experiments made 

 Aug. 3d, 1886, with the same cross indicate that a field of 

 10,500 produces an effect one or two per cent greater than a 

 field of 8000. 



* The results obtained with No. 1 were so variable on these two days that its 

 place among the others cannot be assigned with confidence. Later experiments 

 make its R. P. relatively larger. 



