116 DOVE ON THE ELECTRICITY OF INDUCTION. 



one direction is followed by a wider oscillation in the opposite 

 direction. Let a c (Plate I. fig. 4) indicate the duration of the 

 first current, and a e that of the second ; a b c the curve of in- 

 tensity of the first, a d e that of the second ; and if the superficies 

 a b c = a d e, it is easily seen why the needle, which is only in 

 equilibrium, at the point of section d first moves in the direction 

 of the current a b c, and then in the direction oi a d e ; and 

 that this may even continue for a certain time after the super- 

 ficies a d e has become larger than a b c. The vibration of the 

 needle is more clearly perceptible when the exciting circuit is 

 closed than when it is broken ; but in both cases it is in the 

 direction of the current from the wires. 



13. With this phaenomenon another stands in direct relation. 

 For, as the needle of the galvanometer is set in motion by the 

 difference of two currents, and this difference increases in pro- 

 portion as both currents become stronger, the primary deviation 

 will be augmented by an increase of power in the currents. If 

 this difference arrives at a sensible magnitude, the second cur- 

 rent finds the needle in a less favorable position with respect to 

 the coils of the multiplier than the first did, and the former can 

 for that reason apparently overpower the latter. This was ob- 

 served several times, when calorimotors with very dry plates were 

 used, after the slight vibratory motion had been obtained with 

 previously moistened batteries. In this manner it can therefore 

 be explained why more wires are required to compensate the 

 solid cylinder w-ith strong than with weak currents*. 



14. Although the method of observation by means of two 

 mutually compensating spirals is peculiarly adapted to point out 

 the differences between two currents such as those which were 

 excited, yet it is obvious that the numbers given above, placed 

 in vertical rows, can only express a real numerical relation upon 

 the supposition that the battery was constant in its action. The 

 batteries which were then at my disposal did not warrant such a 

 supposition. By the constant use of loose wires, also, the insu- 

 lation of the iron wires was not at all times the same, for the 

 shell-lac varnish got rubbed off in places. I have therefore en- 

 deavoured to arrange the metals employed in a galvanometric 



• What is here said applies of course only to a current induced by an electro- 

 magnetized bundle of wires acting in opposition to one induced by a solid rod of 

 iron, and not to currents produced by two solid rods of iron acting in oppo- 

 sition to each other. If equilibrium has once been established for these with 

 weak currents, it is not altered by increasing the power of the currents. 



