196 



Mr. W. Stui'ijeon on Electro- Mamets. 



part in the production of electromagnetic rotations; whilst 

 the versatilities of polarity, of wliicli they are susceptible, are 

 eminently calculated to give a pleasing diversity in the exhi- 

 bition of that highly interesting class of phienomena, and lead 

 to the production of others, inimitable by any other means. 



An experiment of this character is noticed in the Phil. Mag. 

 for January 1825 ; but as the arrangement by which it is ac- 

 complished has not yet been published, a description of it in 

 this place may perhaps still be interesting, especially as it 

 affords a clue to several others which niay be exhibited in 

 this curious branch of science. 



Experiment. — Fig. 1. is a representation of the apparatus 

 complete. It consists of a cylindrical rod of soft iron, sup- 

 ported in a vertical position by a 

 round wooden foot, into which its 

 inferior extremity is inserted. The 

 superior extremity of the iron rod 

 passes through the centre of a shal- 

 low wooden dish, which is kept 

 firmly in its place by means of ce- 

 ment. The inside of this dish, and 

 also the iron rod, is covered with 

 sealing-wax varnish. A copper wire, 

 one end of which passes through 

 the bottom of the dish and appears 

 at the upper surface, is wound se- 

 veral times round the iron cylinder 

 between the dish at its upper extre- 

 mity, and the wooden foot in which 

 it is supported. The other extre- 

 mity of the wire terminates in a small 

 cup, as is seen in the figure. 



A stout brass wire, one end of 

 which is screwed firmly into the up- 

 per edge of the wooden dish, rises 



vertically about five inches of its length, at which place it is 

 bent at right angles, and continued in a horizontal direction 

 over the axis of the iron rod. A small brass wire screw, the 

 upper end of which is inserted in a small cup, passes through 



the 



the development of magnetism in soft iron, whether tlic exciting cause 

 be galvanic or any other. And although good annealing is always essen- 

 tial, and facilitates to a considerable extent the display of polarity, that 

 process is very far from restoring to the iron that degree of susccptibilili/ 

 which it frequently loses by the operation of the hammer. 



Cylindric rod iron of small dimensions may very easily be bent into the 

 required form, without any hammering whatever; and I have found that 



small 



