Production of Magnetism by Rotation. 259 



Even at this period it was stated by Mr Babbage, that 

 in all probability similar results might be produced by elec- 

 tricity, if an insulated and electrified metallic needle were sus- 

 pended over a revolving plate of any substance. This expe- 

 riment he did not then make ; but at the commencement of 

 January 1826, while discussing the subject with some friends, 

 he restated his belief, that electricity must produce the same 

 effect ; and finding that they were not so much convinced of 

 this as he himself was, he went home to make the experiment. 

 The apparatus which he intended to use, was a piece of sheet 



brass of the form Q O suspended by silver wire from glass, 



and electrified by contact with excited sealing-wax, and placed 

 above a disc of glass or metal. When glass was used, Mr 

 Babbage mentioned his expectation, that a very slow revolu- 

 tion of the glass would produce one in the electric needle ; 

 while, in the case of the metal, he thought that it might re- 

 quire great velocity, or, perhaps, more than he could give it, 

 and that this would vary, partly according to their relative 

 powers of conducting electricity. 



He performed these experiments, and obtained the results 

 which he had predicted. When the glass disc was very slow- 

 ly turned by the hand, it caused an immediate and very deci- 

 sive revolution in the electrified needle, while copper discs re- 

 quired a much greater velocity. These experiments were re- 

 peated at various times in the presence of several scientific 

 friends, who were satisfied as to the truth of the fact, as well 

 as of its explanation. Mr Babbage has now put up an ap- 

 paratus for more careful experiments, and in order to measure 

 the different conducting powers of various substances. The 

 results of these experiments will soon be communicated to the 

 Royal Society. He suspects that some of the effects ascribed 

 to the magnetism of non-metallic substances may have been 

 produced by electricity ; but he is not yet able to speak with 

 certainty on this point. 



From the preceding historical sketch of Mr Babbage's la- 

 bours, we think it cannot be doubted, that he has the sole 

 and undoubted merit of having been the first to give that ex- 

 planation of the recent experiments of Messrs Barlow, Christie, 

 and Arago, which is founded on the consideration of the time 



