294 M. A. F. Sun dell on Galvanic Induction, 



from the disjunctor to the commutator and the coils were twisted 

 together ; and therefore their influence may be regarded as in- 

 considerable. The tangent-galvanometer was only occasionally 

 inserted in the primary circuit to obtain an approximate value 

 of the intensity of the current ; in the induction-experiments 

 it was taken out of the circuit. The whole deflection is 

 a + a x 4- tf 2 4- b + b 1 + b 2 4- c + c x for the one direction of the pri- 

 mary current, and —a — a^ + a z + b-\-b 1 +b 2 — c + c 1 for the op- 

 posite direction. By addition we obtain 2(rt 2 + # 2 + 6 + 6 1 -fc 1 ). 

 The quantity of a 2 + b 2 -\-c 1 was measured by excluding the 

 inducing coil from the primary circuit. In relation to the 

 diminished resistance the intensity of the current was very great 

 ( = tan52°); yet the deflection (for 128 secondary currents) did 

 not reach half a division of the scale. When the inducing coil 

 was made part of the circuit, the strength of the current was 

 only = tan 28°; and for so feeble a current the sum a 2 + b 2 + c J 

 may be regarded as =0. In the following experiments the 

 coils had this position : the windings of the primary coil were 

 parallel to the #z/-plane \ and the middle spiral of the secondary 

 coil was in the y^-plane, in such a position that it was not inter- 

 sected by any one of the axes. For observing the effect of the 

 second term, this relative position of the coils is the most advan- 

 tageous, as the elements of the integral in expression (14) are all 

 of the same sign. The distance of the centre of the secondary 

 coil from the ^-plane, was a little greater than its diameter. 

 The coils were of the described construction ; their inner radius 

 was 16 eentims., the thickness of the wire 1 millim., and the 

 number of spirals forty-five. The conducting-power of the 

 secondary circuit was =119. The deflections (for 128 cur- 

 rents) to rising numbers of the scale are preceded by the sign 

 +, and those to the opposite side by — . Before every new 

 experiment the inducing current was reversed. 



Experiment 1. 



Deflections , + 13'2 



4-11-2 



4-12-8 



4-12-2 



2. 

 -12-0 

 -12-2 

 -12-6 



3. 



+ 12-4 

 4-12-2 

 4-12-2 



4. 

 -12-6 

 -13-0 

 -11-4 



Means . 4-12-4 

 Experiment 5. 

 Deflections . 4-12-4 

 4-12*0 



4-12-2 



-12-3 



6. 

 -12-8 

 -13-4 

 -12-6 



4-12-3 



7. 

 4-12-4 

 4-12-0 

 4-12-0 



-12-3 



8. 

 -12-4 

 -12-2 

 -11-6 



Means . 4-12-2 -12-9 4-12*1 -12-1 



The mean values of these deflections are 4- 12-25 and — 12*40, 



