1821.] Historical Sketch of Electro-magnetism. 285 



from a battery, were passed, the needle became magnetic. 

 This result was published in the " Allgeraeine Zeitung," of 

 Dec. 2, 1820. Consequently, long after the previous experi- 

 ments of the same kind, though without a knowledge of them. 

 M. Bockman, in repeating and varying these experiments, 

 increased the sine of the helix much beyond what it had formerly 

 been made. When helices, varying from half an inch up to 13 

 inches in diameter, were used, the power of receiving magnetism 

 in the steel needle placed in the axis of the larger did not seem 

 at all diminished. With a helix 34 inches in diameter, the 

 magnetism communicated was much less, and with one 84 inches 

 it was hardly to be perceived. The surface used in these expe- 

 riments was 300 square inches. It was found, on pursuing these 

 experiments, that the needle without the helix was magnetised 

 as well as that within ; that after being fully magnetized, a con- 

 tinuation of discharges weakened its power; that five jars each, 

 of 300 square inches, did not produce with repeated discharges 

 much more effect than one of them ; that a certain thickness of 

 steel in the needle, or bar, was required to produce the greatest 

 effect ; and that on placing a steel needle within a tube of tin- 

 ned iron ; that in a glass tube, and a spiral round it, a discharge 

 caused no magnetism in the needle, but made the tube magnetic; 

 whereas, if the metal tube were lead, then the needle became 

 magnetic. 



M. Von Buch, of Utrecht, while engaged (Jan. 1821) in 

 repeating the experiments of Oersted and others, obtained results 

 according with them, except in one instance, of difference with 

 Oersted. M. Oersted says, that " if the uniting wire be placed 

 perpendicularly to the plane of the magnetic meridian, whether 

 above or below it, the needle remains at rest, unless it be very 

 near the pole : in that case, the pole is elevated when the 

 entrance is from the west side of the wire, and depressed when 

 from the east." M. Von Buch points out that this state of rest 

 does not continue in two of the four positions of the wire. When 

 the connecting wire is beneath the centre of the needle, and the 

 positive current is from east to west, the needle remains 

 unmoved. When the current is from west to east, it performs 

 half a revolution. On the contrary, the connecting wire beino- 

 above the current from east to west, makes the needle turn half 

 way round ; while that from west to east leaves the needle 

 unmoved. M. Von Buch conceives the difference of his results 

 and M. Oersted's to depend upon the superior power of his 

 apparatus ; and indeed it is sufficiently evident that the incom- 



Eleteness of M. Oersted's results depended upon the weakness of 

 is pile. The attractions and repulsions, or the elevations and 

 depressions, he speaks of when the wire was brought near the 

 poles proves the existence of that action which in M. Von Buch's 

 experiments was strong enough to turn the needle round ; and 

 if the position of the wire and needle in these experiments be 



