Mr. W. Sturgeon on Electro- Magnets. 



201 



the macrnetic energies of soft iron. Perhaps the best arrange- 

 ment vv^ould be to have a separate smdl battery to each^; 

 Mr. Marsh has fitted up a bar of non much larger than 

 „,ine with a similar distribution of the conductn.g w^es to 

 that devised, and so successfully employed, by Professoi H nry 

 Mr. Marsh's electro-magnet will support about 560 pmnc s 

 M-hen excited by a galvanic battery similar to mme . i ese 

 two, I believe, are the most powerful electro-magnets yet pi o 

 duced in this country. -p. ^^ 



A small electro-magnet, &' 



which I also employ on 

 the lecture-table, and the 

 manner of its suspension, 

 is represented by fig. 3. 

 The magnet is of cylindric 

 rod iron, and weighs four 

 ounces : its poles are about 

 a quarter of an inch asun- 

 der. It is furnished with 

 six coils of wire in the same 

 manner as the large electro- 

 magnet before described, 

 and will support upwards 

 of 50 pounds. 



I find a triangular gin 

 very convenient for the 

 suspension of the magnet 



in these experiments. A j j- v, • 



stage a a of thin board, supporting two wooden dishes, is 

 fastened at a proper height to two of the legs of the gin. Mer- 

 cury is placed in these vessels, and the dependent amalgamated 

 extremities of the conducting wires dip into it; one into each 

 portion. The vessels are sufficiently wide to admit ot con- 

 siderable play for the wires in the mercury without interrup- 

 tion of contact, which is sometimes occasioned by the swing- 

 inrr of the magnet and attached weight: the circuit is com- 

 pleted by other wires, which connect the battery with these two 

 portions of mercury. When the weight is supported as in the 

 figure, if an interruption be made by removing either ot the 

 connecting wires, the weight instantaneously drops on the table. 

 The large' magnet I suspend in the same way on a larger gm ; 

 the weights which it supports are placed one after another on 

 a sciuare board, suspended by means of a cord at each corner 

 from a hook in the cross piece, which joins the poles ot the 

 magnet. 



• See the Report of Proceedins* at the Royal Institution, in our present 



Numler. — Edit. -tirvi 



N, S. Vol. 1 1 . No. 6f}. March 1 832. 2 D With 



