Foreign Literature and Science. 391 



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tie. Indeed when the current is drawn through the spiral 

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

 dently magnetized.* BibUotheque Univer^le. 



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. 

 xelin, of Bavaria, relative to the magnetism produced by 

 common electricity, and finds that when steel needles are 

 either enclosed in a glass lube 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 magnaetic effects produced by Dr. Hare's Calo- 

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



i 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 nor/A polarity when the turns of the spiral of brass wire 

 ^Dout the glass tube passed from left io H^A/— and soiUh polarity, when they 

 passed from right to le/L The results obtained by me were directly the re- 

 verse of these ; and in my exj>eritiients, (which have been often repeated in 

 the presence of Professor Sillimau,) (he end of the needle connected with 

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

 passed from left to righl^ and north polarity when they passed from rigki to 

 /f/?.— I will now add the result of an experiment which has been performed 

 ^ince the publication of my paper. A brass wire was wound about a ^lass 

 tube from Iffg to rights until half of the tube was covered by the wire, when 

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

 aiaining half of the tube from right to left. A needle, free from magrnetism, 

 navino; been encJjQsed within the tube, the ends of the spiral were connec- 

 ted with the opposite poles, and the plates immersed, ^inJ ag:ain raised from 

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

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

 ^xperimept was. often repeated, and the ^ame results obtained. 



G- T. BO^VKN 



Sfptembcr Uh^ 1822. 



