This section is from "Scientific American Supplement Volumes 275, 286, 288, 299, 303, 312, 315, 324, 344 and 358". Also available from Amazon: Scientific American Reference Book.
The merits of a brake in which electric apparatus is used, that has been adopted by one large railway company, and is about to be used on the State railways, as well as the fact that arrangements are being made to introduce it in England, demand consideration. It may be that modifications will, under different circumstances, be introduced, or that the system will ultimately be found too cumbersome or too delicate, but before criticism it is necessary to know something of the apparatus. We therefore endeavor to give somewhat in detail the arrangement adopted by M.L. Regray, chief engineer of the Chemin de Fer de l'Est, the electrical system being that of M. Achard. An electro-magnet, A, is suspended on a hinged axis, so that the poles of the magnet have for armatures cylinders of metal fixed upon the axle of the carriage. Suppose now the poles, D D, of the magnet brought into contact with the revolving armatures, the friction between them causes the magnet to revolve. The chain attached to the brake is fixed to the extended axle of the magnet, and consequently when that axle revolves is wound up, bringing the brakes upon the wheels. The friction between the poles and the armature depends upon the strength of the magnet, and this can be regulated at will from a maximum to a minimum. But it will be well to trace the whole action. The electric current may be obtained by means of Planté secondary cells charged by Daniell's cells - in other words, one or two Daniell's cells are constantly in action charging three or six Planté cells, and it is the Planté cells that are called into action to electrify the magnet. The battery is carried in a box in the brake van. The engineers, however, seem to prefer that the current be obtained by means of a small Gramme machine, driven direct by a Brotherhood three-cylinder engine, the steam for which is obtained from the locomotive. The velocity and hence the current of the Gramme machine can be regulated, and so the action of the brakes. M. Achard prefers the Planté cells; he informs us that he has tried the Faure battery, but the results obtained were not satisfactory. The regulator, R², consists of a cylinder of wood around which, as shown, wire is wound. The length of this wire in the circuit, increasing as it does the resistance of the circuit, determines the current to the electro-magnet. The action is as follows: When it is necessary to apply the brakes, a simple pressure of a key or the turn of a handle sends the electric current into the wires of the electro-magnet. An attraction immediately takes place, and the poles and armatures are brought into contact. The friction between these causes the revolution of the magnet, the winding of the chain around the axle, and the application of the brakes. The whole of the brakes of the train enter into action at one and the same time. The brakes are taken off by stopping the current, and a small spring pulls and keeps the magnet from the armatures. A frame - also carriages - fitted with this brake, are shown by the Compagnie des Chemins de Fer de l'Est, which company also shows several other pieces of interesting apparatus, one of which is a carriage fitted with elaborate mechanism, in which electricity plays, perhaps, but a subsidiary part, to obtain the traction of the train under varying circumstances, the pressure on the buffers when stopping, and various phenomena connected with the engine. - The Engineer.