494 Intelligence and Miscellaneous Articles. 



ON MAGNETIZING STEEL NEEDLES BY THE CURRENT OP A LEY DEN 



JAR. BY DR. PAALZOW. 



From the fact that a steel needle, by the discharge of a Leyden 

 jar, may be abnormally magnetized, that is to say in a direction 

 contrary to that required by Ampere's rule, Savary and Helmholtz 

 concluded that there must be an alternating motion of the electricity 

 in the circuit of a Leyden jar. I imagined I had found in the phe- 

 nomena of Geissler's tubes a means by which it could be decided 

 whether the discharge was simple or alternating ; with its help it 

 could be shown whether the occurrence of abnormal magnetism 

 actually depended on a change in the direction of the current. 



The proof could be given by magnetizing with currents which, 

 according to the indications of the tubes, had a single direction. 

 Under these circumstances only a normal magnetism should be 

 observed ; and when abnormal magnetism occurred, the indications 

 of the tube ought to be those of alternating discharge. 



I accordingly induced Dr. von Liphard to investigate the magneti- 

 zing of steel needles by the current of the battery. He found that, 

 so long as the Geissler's tubes indicated with certainty a single dis- 

 charge, abnormal magnetism was never observed ; and that when- 

 ever abnormal magnetism occurred, the luminous phenomena indi- 

 cated alternating discharges. 



But the proof that abnormal magnetism is to be ascribed to cur- 

 rents in opposite directions may be drawn from the needles them- 

 selves. Wiedemann, in his investigations on the magnetization of 

 steel bars (Poggendorff's Annalen, vol. c. p. 241), has given a method 

 for deciding whether a magnetic or unmagnetic needle was previously 

 magnetic or had a different magnetism. It appeared to me possible 

 to show by the aid of these means that the abnormally magnetized 

 needles had been previously normally magnetized by the same dis- 

 charge of a battery, and that in fact a demagnetization had actually 

 taken place. 



In common with Prof. Wiedemann I commenced these investigations, 

 and have since continued them. Of the modes of testing, that was 

 chosen whichis described in the above treatise in the followingwords: — 



" If the magnetism in a steel bar had been partially or totally with- 

 drawn, or even completely reversed by a current opposite in direc- 

 tion to the original magnetizing current, it regained, on being struck, 

 a part of its first magnetism. Hence it is possible in this way to 

 prepare an unmagnetic bar, which by agitation becomes magnetic. 

 In this case the bar can of course be placed at right angles to the 

 magnetic meridian, and thus withdrawn from the influence of the ter- 

 restrial magnetism." 



In these experiments it was shown that perfectly unmagnetic 

 needles, which also remained unmagnetic when they were struck 

 before being magnetized, assumed normal magnetism when struck 

 with unmagnetic substances, after they had been abnormally mag- 

 netized by the discharge of a Leyden battery. In these experiments 

 the circuit consisted of short good conducting wires, between which 

 a Riess's air thermometer and a short magnetizing spiral of 27 turns 

 were coiled. 



