128 Prof. Reich on the Repulsive Action of a 



be estimated to a tenth, and the force therefore to 0*0001 of 

 a milligramme. 



I first tried the effect of magnets upon one of the balls 

 which had been employed in the determinations of density, 

 and which consisted of tin mixed with 10 percent, of bismuth 

 and about 2 per cent, of lead. Magnet bars on being brought 

 up in a horizontal direction to the case near a ball produced 

 a very distinct repulsion, both when the north and the south 

 pole were brought near. But when several similar bars were 

 brought near, half with their north and the other half with 

 their south poles, there was no effect perceptible, or merely a 

 slight one, arising from the inequality of the magnets em- 

 ployed. A horse-shoe magnet with its two poles was just as 

 ineffective. A four-pound magnet bar belonging to a mag- 

 netometer was brought as close to the south ball as the wooden 

 case would permit, and in a direction perpendicular to the 

 rod. The rod previously stood at 41*50 of the scale, the ap- 

 proach of the north pole re. laved it 5314'; the south pole 

 then raised it to 55*45, and the north pole again brought it to 

 54*05. After removing the magnets, the position of rest found 

 was 42*80. If we take the mean from the first and last posi- 

 tion of rest with the magnets removed, and also with the north 

 pole brought near, we obtain — 



Repulsion by the north pole 11*445 divisions of the scale, 

 south pole 13*300 



The diflference may be owing to unsymmetrical distribution 

 of the magnetism in the bars. 



As is well-known, the repulsive action of a magnet upon 

 bismuth had been observed ; I therefore had a ball made of 

 pure bismuth of the same weight, and hung it in the place of 

 the one hitherto used upon the south extremity of the rod of 

 the torsion-balance. 



The position of rest of the rod with the magnet at a distance 

 was observed to be — 



Divisions of scale. 

 previously . . 11*200 

 subsequently . _9*775 Time of vibration. 

 mean . , . 10*488 350*5 seconds. 



North pole close to the case . . 69*250 280*8 



at 10 millims. distance 43*670 307*4 



at 30 millims. distance 21*205 333-7 



This gives — 



