Dr, Tyndall on the Laws of Magnetism. 283 



to a current of 25° was taken as a standard. A certain weight 

 was laid upon the scale-pan, and a cm-rent somewhat greater 

 than 2o was sent round the magnet. The ball was brought 

 down upon the leaf or leaves which measured the distance from 

 the pole, and the rheostat was slowly turned until the ball gave 

 way. If this occurred at 25°, the right weight for the distance 

 m question had been chosen. Su])pose, however, that the ball 

 presei-ved its hold till the current was damped to 23-'; it is plain 

 that the weight chosen was too small, and a little must be added. 

 If the ball, with this addition to the weight, yielded before it 

 reached 25°, then the weight added was too large. Thus by a 

 method of approximation similar to that above described, the 

 exact weight due to a certain distance and to a magnetic power 

 of 25 was obtained. From the description this will appear a 

 circuitous process, but it is not so practically. With a little ex- 

 perience the proper weight can be ascertained with great dispatch. 

 2o. The following table contains a series of experiments made 

 in this manner with ball No. 2 : — 



Table VII. 



Strength of current 25°. Paper ToVodth of an inch thick. 



Ball No. 2. 



