With the assistance of the magneto-electric machine, telegraphic communication may be conducted without the assistance of a battery. It has also been applied to the art of electro-plating by Mr. J. P. Woolrich, of Birmingham; and whilst visiting that place, the author had the opportunity of witnessing the arrangement employed. It consists of a very powerful magneto-electric machine turned by a steam-engine, and connected with the large troughs containing the silvering solution. If it is required to deposit a thin coating of silver on the article, a short period suffices for the action of the machine, whilst a thick deposit of the precious metal is only obtained by the constant operation of the magnets for several hours. At Mr. Woolrich's factory, the goods which were being coated with silver were all kept in motion, moving slowly backwards and forwards in the trough by means of an eccentric connected [Page 246] with the same steam-engine that worked the electro-magnetic machine. (Fig. 240.) [Illustration: Fig. 240. Silvering and plating by the magneto machine, turned by a steam-engine.] The magneto-electric telegraph patented by Mr. Henley in 1848, offers another example of the application of the electric current induced in electro-magnetic coils, when they rotate in close proximity to the poles of a powerful steel magnet. This telegraph is now in constant use by the English and Irish Magnetic Telegraph Company, through a distance of more than 2100 miles. The whole length of wires in use amounts to the astonishing quantity of 13,900 miles, of which 6350 miles are hidden underground, and 7500 conducted above. This telegraph is considered to be one of the simplest and most economical yet brought into practical working. [Page 247] CHAPTER XX. DIA-MAGNETISM. At the end of the chapter devoted to the subject of light, will be found an experiment devised and carried out by Dr. Faraday, in which it is shown that if a bar of a peculiar glass (called after the inventor, _Faraday's heavy glass_, or silicated borate of lead) is subjected to the inductive action of a very powerful electro-magnet, that it has the power of changing the direction of a ray of polarized light transmitted through it. This effect is not confined to the poles of an electro-magnet, but is also perceptible (though in a diminished degree) with ordinary magnets.