REPORT OF MR. ROBERT B. LINES.
455
"line clear,” there is no effect produced. If, on the contrary, it is turned to " arrest,” the sheet of brass is in communication with a source of electricity, and, on the passage of the locomotive, the metallic brush completes the circuit through the helices of the magnet, the armature is repelled, and the whistle is made to sound in the manner described.
This apparatus is said not to have been at all deranged by the shock of contact, and the brushes, after eight months’ usage, show scarcely any traces of wear.
The contact between the rails is the one adopted by the Compagnie du J\ T o?'d. Where very heavy snow-falls or other obstructions are to be feared, however, the contact might easily be placed at the side of the engine, at a convenient height from the ground.
It was feared, at first, that owing to the speed of trains the contact would not be sufficiently lasting to produce the desired effect, and accordingly the first trials were made with fixed contacts of over four metres in length, which permitted a contact lasting from one-fourth to one-fifth of a second at the highest speed. It was found, however, that a length of two metres in a fixed contact was sufficient to give the necessary signal, and this is the length adopted.
Various applications of the apparatus (in its entirety) are suggested by the inventor, not only for railways, but for the service of mines and the marine. The important uses to which the contact alone may be adapted will probably suggest themselves in the course of the following pages.
The apparatus of Group II, above described, is employed for the purpose of giving information merely of the position of a switch or semaphore. We now come to subdivision b :—
Instruments by which the position of semaphores may be changed or controlled at a distance through the medium of electricity.
Mr. W. H. Preece, the well-known Superintendent of British Postal Telegraphs, himself the inventor of a very ingenious system of signals, which will be hereafter described, says, in an able review of this subject, published in 1865 : "If it were possible to work an out-door signal by electricity the system would be perfect, but inasmuch as the power of electricity is but circumscribed, we have not yet attained that