Masterpieces of Science 



By an attentive perusal of the original account 

 of the experiments of Arago, it will be seen that, 

 properly speaking, he made no electro-magnet, 

 as has been asserted by Morse and others; his 

 experiments were confined to the magnetism of 

 iron filings, to sewing needles and pieces of steel 

 wire of the diameter of a millimetre, or of about 

 the thickness of a small knitting needle. 



Mr. Sturgeon, in 1825, made an important 



Fig. 4 



step in advance of the experiments of Arago, and 

 produced what is properly known as the electro- 

 magnet. He bent a piece of iron wire into the 

 form of a horseshoe, covered it with varnish to 

 insulate it, and surrounded it with a helix, of 

 which the spires were at a distance. When a 

 current of galvanism was passed through the helix 

 from a small battery of a single cup the iron wire 

 became magnetic, and continued so during the 

 passage of the current. When the current was 

 interrupted the magnetism disappeared, and 

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