Magnetism on a permanent Electric Current. 317 



Gold Foil, No. 30 A (semicohesive?). 



Length of strip when weighed =5*76 centims. 



Width „ ,, =1-085 centim. 



Area, including projections . =7*36 square centims. 



Weight = "161 grm. 



.-. Thickness = -001129 centim. 



With this plate, 



M. C. 







MxV 



E' ' 



123 x 10 10 



124 „ 



128 „ 



April 20th, 6520 k x tan 48 38 

 „ 23rd, 6600 „ „ 31 30 

 „ „ 6600 „ „ 40 39 



Mean' . . =1250 x 10 9 



This value is about 20 per cent, lower than the mean of 

 those obtained with the three plates, Nos. 4, 5, and 6, previ- 

 ously used. The discrepancy was so great that another plate 

 was made with a strip cut from the same sheet as No. 30 A. 



Gold Foil, No. 30 B (semicohesive ?). 



Length of strip when weighed =5*69 centims. 



Width „ „ =1*08 centim. 



Area, including projections . =7*33 square centims. 



Weight = *149 grm. 



.-. Thickness = -00105 centim. 



It will be seen that the strips A and B, cut from similar 

 positions in the same sheet of metal, differ about 7 per cent, 

 in mean thickness. The importance of this fact has already 

 been pointed out. The difference in thickness thus found 

 was so great that I at first supposed a mistake must have 

 been made in weighing the first strip, thereby giving too large 

 a value for the weight. I therefore removed the strip from 

 the glass plate and weighed it again. The result confirmed 

 the original value obtained. 



With the new plate, No. 30 B, I found:— 



MxV 

 E' ' 

 139 x 10 10 

 141 .. 



M. 



C. 



April 26th, 6760 



k x tan 6^ 



)) )) 



„ „ 39 26 





Mean . . 



= 1400xlO y 



This value is much nearer those obtained with the plates 4, 

 5, and 6 ; but even now there is a discrepancy of 8 or 10 per 

 cent. Without discussing this matter any farther at present, 

 I pass on to tell what has been observed with 



Phil. Mag. S. 5. Vol. 10. No. 63. Nov. 1880. 2 A 



