of Magnetic and Diamagnetic Bodies. 49 



B. An excitation from the middle to the ends occurs if we 

 place a bar in an electrical spiral ; but in this case all the sub- 

 stances must gain the same polarity as the iron. 



To prove that, I placed a thick bar of bismuth in a very strongly 

 acting spiral, which was excited by four cells of Mr. Grove, 

 eveiy one of 12 square inch of platinum plate. I set this spiral 

 on one side, and near to a little declination-needle suspended 

 by a silk thread, and I compensated its effect by a steel magnet 

 which I adjusted on the other side of the needle till the latter was 

 returned to its first place. When I withdrew the bismuth bar 

 out of the spiral, then the needle declined in favour of the com- 

 pensating magnet ; but if I restored it again in the spiral, then 

 the needle declined in favour of the spiral. Unfortunately the 

 poverty of the physical establishment of our university did not 

 allow me to test other substances than the bismuth, but I shall 

 supply this defect as soon as it is to be done. You will allow me 

 the consequence, — that diamagnetism and magnetism are only 

 modifications of the same power, which are produced partly by 

 the different coercive power of the substances, partly by the dif- 

 ferent manner of excitation. 



Applying the former to the theory of Ampere, T wti^ 'startled, 

 because it has hitherto taught only that currents which are 

 parallel and directed in the same way attract, but if they are 

 parallel, and not directed in the same manner, they are repulsive ; 

 therefore, that a current, moving in the direction of the hand of a 

 watch, in a spiral produces a south pole on the entrance point in 

 the spiral, but a north pole on the egression point. Hitherto, 

 only such spirals have been constructed in which the cui-rent in 

 every winding shows an equal intensity. 



But I tried to arrange spii-als of the following kind : — One 

 of them is in such a way constnicted, that on two copper wires 

 are soldered to each of them fifteen thin wires covered over with 

 silk. The first winding backwards over the copper wire, i. e. the 

 first convolution of tlie helices, beginning at the end and pro- 

 ceeding towards the centre, is with all the fifteen wires; the 

 second winding is only wovmd with fourteen threads, whilst 

 the fifteenth is carried along the axis, &c. ; consequently every 

 convolution of the fifteen windings has a thread less, and the ends 

 of all the other threads have the direction of the axis. The 

 ends of the fifteen threads are soldered in the middle, and the 

 two thick wires, without touching each other, are so bent, that 

 they can be suspended in the little cups of the apparatus of 

 Ampere ; then a current, passing through the sj)iral, will divide 

 it.self in such a manner that it is most strong on the external 

 ends of the spiral, but decreases more and more to the middle. 



Phil. Mag. S. 4. Vol. 1. No. 1. Jan. 1851. il 



