Foreign Literature and Science. 391 



lie. Indeed when the current is drawn through the spiral 

 by taking sparks from the conductor, the steel becomes evi- 

 dently magnetized.* Bibliotheque Universelle. 



34. Electro-Magnetism. — Professor C. W. Bockman, of 

 Carlsriike Baden, in a memoir addressed to Prof. Pictet, 

 states that he has repeated the experiments of the Chev. 

 Yelin, of Bavaria, relative to the magnetism produced by 

 common electricity, and finds that when steel needles are 

 either enclosed in a glass tube or enveloped in waxed cloth, 

 silk, wood, ivory, or paper, and a wire turned spirally round 

 the envelope, the steel is always magnetised when a Leyden 

 bottle is discharged, or when strong sparks are passed 

 through the spiral wire. He has demonstrated that the 

 magnetic force increases with the electric tension or num- 

 ber of discharges to a certain extent, when it acquires a 

 maximum. 



It seldom went beyond fifteen or twenty discharges, with 

 common electric bottles. The magnetism appears also to 

 be increased by increasing the number of turns in the spiral 

 wire. 



* After the paper, " On the magnetic effects produced by Dr. Hare's Calo- 

 rimotor," was printed, Professor Silliman received the notice in the text. 

 1 was entirely ignorant of the experiments of Mr. Van Beck, when mine 

 were undertaken, and all the information 1 now possess on the subject is de- 

 rived from the above notice. There seems, however, to have been a difference 

 in the results obtained by Mr. Van Beck and myself; that gentleman found 

 that the end of the needle which was connected with the zinc plates of his 

 battery, acquired jiort/i polarity when the turns of the spiral of brass wire 

 about the glass tube passed from left to right — and south polarity, when they 

 passed from right to left. The results obtained by me were directly the re- 

 verse of these ; and in my experiments, (which have been often repeated in 

 the presence of Professor Silliman,) the end of the needle connected with 

 the zinc plates, always acquired south polarity when the turns of the spiral 

 passed from left to right, and north polarity when they passed from right to 

 left. — I will now add the result of an experiment which has been performed 

 since the publication of my paper. A brass wire was wound about a glass 

 tube from left to right, until half of the tube was covered by the wire, when 

 the direction of the spiral was changed, and the wire wound about the re- 

 maining half of the tube from right to left. A needle, free from magnetism, 

 having been enclosed within the tube, the ends of the spiral were connec- 

 ted with the opposite poles, and the plates immersed, and again raised from 

 the fluid. On removing the needle, its two ends were found to have ac- 

 quired north polarity, while the middle had acquired south polarity. This 

 experiment was often repeated, and the same results obtained. 



Tx. T. BOWEN. 



6'£/)/m&cr4//(, 1822. 



