SECT, xxxm.] AND ELECTEICITY. 369 



The character of the force thus impressed upon the flint- 

 glass, or silico-borate of lead, is that of rotation, for the 

 stopping and renewing of the electric or magnetic current 

 has the same effect as the revolving motion of the eye-piece 

 in making the light alternately appear and vanish. Accord- 

 ingly Dr. Faraday found that, when the electricity flowed 

 In one direction, the rotation of the light was right-handed, 

 and when in the other direction the rotation of thr ray was 

 left-handed. The rotation increased with the length of the 

 flint-glass and silico-borate of lead, and also with the inten- 

 sity of the electricity. 



Heavy glass, or silico-borate of lead has the property, 

 more than any other substance, of making light rotate under 

 electro-magnetic influence ; but many substances have the 

 property, as flint and crown glass, rock salt, all the fires 

 and essential oils, water, and many liquids, but none of the 

 gases possess it. 



Of the brilliant discoveries of Dr. Faraday, none are more 

 worthy of admiration than those he has made with regard 

 to the diamagnetic properties of matter. 



He has found that all bodies are subject to the action of 

 the magnetic force, but that it is very different in different 

 substances; for example, if a bar of iron be freely sus- 

 pended between the poles of an electro-magnet, it will be 

 attracted by both poles, and will rest in the direction of 

 the axes between them, that is, in the line of force ; but, 

 if a bar of bismuth be suspended in the same manner, it 

 will be repelled by both poles, and will assume a direction 

 at right angles to that which the iron took ; thus the same 

 force produces an opposite effect upon these two' metals. 

 Substances affected after the manner of iron are magnetic ; 

 those affected after the manner of bismuth are said to be 

 diamagnetic. All substances come under one or other of 

 these two classes; many are magnetic; but the diamag- 

 netic substances are innumerable, almost all the bodies on 

 earth many of the metals, acids, oils, sugar, starch, wood, 



B B 



