646 HENRY A. ROWLAND 



dielectric, but also on the nature of the latter, air or vacuum producing 

 the least condensing effect, and glass, sulphur, etc., a greater one. 



To complete his mental vision of an electrified system, it was neces- 

 sary for him to test in a very complete manner the idea that positive 

 and negative electricities are generated in equal quantities. To accom- 

 plish this, he erected a room of twelve feet on a side out of a frame- 

 work covered with tinfoil, and the whole insulated. By generating 

 electricity inside of it, he was able to prove in a more complete manner 

 than had been done before that we never generate positive electricity or 

 negative electricity by itself, but always in equal quantities together. 

 Every complete electrostatic system contains equal quantities of posi- 

 tive and negative electricity, which are separated by a dielectric, through 

 which they are connected by the lines of electric induction, whose ten- 

 sion produced electric attraction. 



To-day, when the mathematics of Maxwell have added clearness to the 

 subject, we see every electrostatic system made up of minute and equal 

 portions of positive and negative electricity, connected together by 

 tubes of induction as by elastic bands, these tubes repelling each other 

 laterally, so as to be held in position, we know that the attraction of all 

 electrified bodies is accounted for by such a system, which was roughly 

 conceived by Faraday, but in which the positions and form of every lino 

 can now be calculated. 



It is impossible, on the present occasion, to follow Faraday through 

 all his researches on the different forms of electric discharge, and his 

 continued researches on electrolysis; but I will pass immediately to two 

 of his greatest discoveries, the action of magnetism on light and diamag- 

 netism. In his researches on optical glass he had discovered a variety of 

 heavy glass, called silicated borate of lead. On placing this between 

 the poles of a magnet, and looking through it along the lines of force, 

 he found that the plane of polarization was rotated. 



Using other substances, he found that most of them had some effect 

 of this kind in the magnetic field. The laws of the magnetic rotation 

 he found very different from those of the ordinary rotation of turpen- 

 tine or sugar, and altogether it forms a most interesting and important 

 experiment when considering the theory of magnetism. 



Not content with discovering this law with his piece of optical glass, 

 he now sought to discover whether there was any force of attraction 

 or repulsion between it and the magnet. Hanging it up between the 

 poles, he discovered that as iron was attracted by a magnet, so the heavy 

 glass was repelled. He called this property diamagnetism, and showed 



