212 



ON MAGNETISM. 



unmagnetized steel needle to the end nearest to itself, 

 and thereby magnetizing that needle. And in like 

 manner, if a soft iron bar be presented to it, it converts 

 it for the moment into a magnet in a similar state. It 

 is therefore easy to conceive that the galvanic current 

 may be able to produce analogous effects. 



The best form of wire for this purpose is a long 

 spiral. In Figure 70 is exhibited a simple spiral : but 



Fig. 70. 



the wire may be carried round and round so as to form 

 numerous layers, care being taken that the wire is 

 turned round always in the same direction. Such a 

 spiral constitutes a kind of magnet, which, though 

 acting feebly on external objects, is sometimes useful. 

 But its magnetic effect in the interior of the coil is 

 powerful. Conceiving a mass of red magnetism in the 

 interior, the imaginary insect which we have cited, in 

 crawling along the wire from the graphite end, with his 

 face towards the nearest part of the red mass, would in 

 every part of the spiral have his left hand towards the 

 graphite : and therefore the attraction of every part of 

 the coil tends to draw the red magnetism towards 



