Magneto-electric Phenomenon. 



221 



that, on breaking the circuit, the impulse is truly proportional 

 to sin 2a. Examination shows that the negative impulses, 

 though in reality equal to the others, are apparently much less 

 in amount, that they are not even in proportion, and not only 

 this, but that the corresponding values on either side of 45° are 

 not the same. This want of symmetry is clearly shown by 

 fig. 1. The discrepancy is due to the fact that the disk is 

 brought to rest by the damping action of the field as well as 

 by the torsion of the wire, and that the damping action is 

 greater as the angle is less, being : : cos 2 a. 



Fig. 1. 



I thought it would be interesting to determine to what 

 angle the disk would be thrown if the torsion of the wire did 

 not act. I therefore suspended, instead of the disk, the coil 

 used in the absolute experiments by a silk thread, adjusted the 

 lower card by the method of no throw, and brought the index 

 to rest successively over 10°, 20°, 30°, &c. up to 90°. The 

 index came to rest at the series of positions shown in column 2 

 of the following Table: — 



Table II. 



Pointer fell 



From 



To 



10 



36 



20 



6 



30 



10 



40 



13 



45 



16 



50 



18 



60 



22 



70 



29 



80 



39 



The same results are shown graphically in fig. 2. It is 



