Maqneto-Electric Induction . 



455 



were obtained after the completion of the set of experiments, 

 by resetting the plate to the proper distances, to see if there 

 had been any great change in the power of the magnets or 

 the torsion of the thread. 



On plotting out the curve of distance we find line 2, fig. A 

 (p. 453). 



III. Valuation in the Diameter of the Disk. — For the study 

 of this effect the same apparatus was used again, the only 

 difference being that the magnet was only 2 inches long ; and 

 a series of disks of copper were cut of the same thickness as 

 that used for finding the law of distance. Thev were held in 

 the same way — by a drop of weak gum on the under surface 

 of the ebonite disk. The distance was kept constant, namely 

 3 millims. In Table III., column Diam. gives the diameter 

 of the disk in inches, column A the corrected mean deflexion 

 of about four observations, column T the time of one revolu- 

 tion of the worm-wheel, got by taking the time of ten or 

 twenty turns, during which the angles are read ; and column 

 A' is equal to A x T, and represents the torsion for constant 

 velocity. 



Table III. 



Diam. 



A. 





o 



100 



03 



1-25 



0-9 



' 1-50 



2-6. 



1-75 



6-5 



200 



fl0-7 

 \l2-5 



2-25 



f21o 

 1214 



2-50 



30-8 



275 



38-7 



3-00 



461 



2-25 



50-9 



3-50 



50-0 



A' = AxT. 



2-53 

 2-79 

 2-82 

 283 

 [3-99 

 1 3-90 

 4-02 

 4-09 

 403 

 406 

 4-01 

 4-00 

 3-90 



18 



r 42 



1 48 



87 

 124 



157 

 184 

 203 

 218 



759 



511 



332 



395 



69 



75 



43 



53 



1 



1 



9 



6 



4 



The curve 3 in fig. A is the graphic representation of the 

 above relationship. As was to be expected, there is a point 

 of contrary flexure at about the region where the disk has a 

 diameter equal to the length of the magnet. 



IV. Effects of Cuts in Disks. — The same apparatus was used, 

 and copper disks 3 inches in diameter, of the same thickness 

 and at the same distance from the 2-inch magnet. In Table 

 IV., A is the observed angle, T the observed time of rotation, 

 and A' is the product of A and T, and is proportional to the 

 force for a constant rate. 



The attached figures represent the way in which the disks 

 were cut. 



