Magnetism on a permanent Electric Current. 307 



for different metals, but for any particular metal it seems 



much more nearly a constant than the ratio — =^ — given above 

 would be. 



It may seem to those who read the following pages that an 

 unnecessary amount of study has been devoted to gold. It 

 must be remembered, however, that many readers of my pre- 

 vious article were not fully convinced by the evidence there 

 adduced that any really new principle had been discovered, 

 thinking that the explanation of the phenomenon described 

 was possibly to be found in some such fact as the state of 

 mechanical strain into which the strip of gold leaf would be 

 thrown in its endeavour to move across the lines of magnetic 

 force, in obedience to the perfectly well-known laws of the 

 action of magnets on conductors bearing currents. This being 

 the case, it seemed desirable to make experiments with several 

 strips of the same metal, and determine whether the ratio 



Mx V 



— =^— would prove to be a constant for all. The dimensions 



of many of the strips used, of whatever metal, are given below; 

 and in order that the conditions to which they were variously 

 subjected may be more fully understood, there are given in 

 many cases the strength of the magnetic field in absolute 

 units and the strength of the primary current through the 

 strip, the latter being expressed in terms of the constant k of 

 the tangent-galvanometer used to measure it. This constant 

 there has been no occasion to determine exactly ; but it is 

 about -07. 



It will probably be readily admitted that the results obtained 

 cannot be accounted for without admitting substantially all 

 that was really claimed in the previous article. Even if no 

 such quantitative investigation had been made, however, there 

 would still be one fact inexplicable on the theory of an acci- 

 dental cause for the phenomenon under consideration. The 

 arrows in fig. 2 show the direction of the transverse current 

 relatively to the direct current in gold, the magnetic pole S 

 being a south pole, i. e. the pole attracting the north-pointing 

 end of a needle. This relation between the directions of the 

 two currents and the magnetic force is the same in all of the 

 four gold plates which have been examined in this particular. 

 The same uniformity is observed in the four silver plates, and 

 the three iron plates, which have been tested in the same way. 

 With the two plates of tin which have been examined there 

 has been a trifle of uncertainty upon this point, as the effect 

 in this metal is at best very small ; but this uncertainty is 

 hardly sufficient to cast doubt upon the correctness of the rule 



