OF ARTS AND SCIENCES. 449 



in the armature, when currents were sent through the primary coils in 

 the same and in opposite directions, with the following results. The 

 armature being placed at the middle of the bar, and parallel currents 

 being sent through the primary coils, there was no deflection of the 

 galvanometer. When opposite currents were sent througli the primary 

 coils, the deflection was about GO mm. A current through a single 

 coil gave a deflection of 32 mm., or very nearly the mean of the other 

 two. A very slight correction was made, due to the direct action of the 

 primary on the secondary coil. 



These experiments then gave the same results as those at which we 

 had arrived- theoretically, showing most conclusively that this is the 

 correct explanation of Jamin's results. 



As a further proof of the illegitimacy of Jamin's conclusions, and a 

 proof which is independent of the secondary coil and galvanom- 

 eter previously used, I have, using Jamin's apparatus, with the single 

 modification of making the armature quite long in proportion to its 

 diameter, and approaching it to the bar always in such a position that 

 its longer axis shall be parallel to the axis of the bar, succeeded in 

 obtaining results directly opposed to those of Jamin, and in harmony 

 with the result of my previous experiments. 



In order to make the experiment plain, let us see what ought to be 

 the condition of the Amperian currents in such an armature. 



Since it is quite long in proportion to its diameter, the Amperian 

 currents would tend to arrange themselves at right angles to its axis ; 

 and, approaching the armature in the manner described, the currents in 

 the armature would be parallel to those in the bar. With such an 

 armature, therefore, we ought to have a greater attraction when the 

 currents through the primary coils are parallel than when opposed. 



That this is the case 1 have proved by the following experiment : 

 A small armature of chemically pure iron was made, with a length of 

 6.5 mm. and diameter of only .8 mm. This was approached, with its 

 axis parallel to the bar, always to the middle of the bar, since it is at 

 this point that the difference in effect of parallel and opposed currents 

 ought to be most marked. 



The actual strength of the magnetism of the bar at this point could 

 be varied by moving the inducing coils to or from the middle point, 

 and in this way the intensity was made such that when parallel cur- 

 rents were sent through the coils the armature was supported by the 

 bar. Upon reversing the current in one of the coils and again ap- 

 proaching the armature, the attraction of the bar was insufhcient to 

 support it in this position, although it would assume a position at right 

 VOL. X. (n.s. n.) 23 



