The Boy's Playbook of Science / Including the Various Manipulations and Arrangements of Chemical and Philosophical Apparatus Required for the Successful Performance of Scientific Experiments in Illustration of the Elementary Branches of Chemistry and Natural Philosophy

by John Henry Pepper

Ingeniously-constructed lightning-conductors are attached to the posts which carry the wires, so that in case of a storm, the natural electricity is conveyed to the earth, whilst the voltaic electricity artificially produced pursues its own course without deviation. Protectors are also required for the instruments at the stations, and the plan devised by Mr. Highton is thus described by the inventor:—

"A portion of the wire circuit—say for six or eight inches—is enveloped in blotting-paper or silk, and a mass of metallic filings, in connexion with the earth, is made to surround it. This arrangement is placed on each side of the telegraph instrument at a station. When a flash of lightning happens to be intercepted by the wires of the telegraph, the myriads of infinitesimally fine points of metal in the filings surrounding the wire at the station, on having connexion with the earth, at once draw off nearly the whole charge of lightning, and carry it safely to the earth."

THE INSTRUMENTS TO BE WORKED—THE BELL AND THE TELEGRAPH.

The bell or alarum resembles in construction that of an ordinary clock, and is in fact a piece of clockwork wound up and ready to ring a bell, when the detent or preventive is removed. The detent is connected with a piece of soft iron placed before an electro-magnet, and directly the current passes, the electro-magnet attracts the soft piece of iron attached to a perpendicular lever which the bell-crank lever rests upon; the detent is removed, and the bell rings, and again stops when the current of electricity ceases to pass.

One of the most simple alarum clocks is a common American clock, wound up daily. A small electro-magnet surrounded with thick wire is placed below a moveable piece of tinned iron, so that when this is attracted, the fly of the clock is released, and its bell tolls unceasingly while the magnet is excited. This arrangement is employed by Sir W. O'Shaughnessy in the Indian telegraph system. (Fig. 212.)

Fig. 212.

a. The soft iron tinned, which is attracted to the electro-magnet b, and liberates the detent.

It will readily be comprehended from this description that the alarum is sounded by ordinary mechanism, and that the duty of the current of the electricity is simply comprised in the act of removing the lever and liberating machinery, which may be large or small; and if it were thought necessary, the bells of the great clock-tower of the Houses of Parliament, which chime the quarters, or even "Big Ben" himself (when his constitution is restored), could be rung by a person at York or Edinburgh, supposing wires, batteries, and a powerful electro-magnet with a detent mechanism for the bells, were properly arranged and connected with the clockwork.

In certain cases, Mr. Charles V. Walker states that a single and distinct wire is used for the bell only, with his special mechanism, called the ringing key. If the bell was always on the same wire as the needle-coil, the bell would not only call the attention of, but seriously annoy the clerk (unless, of course, he happened to be a very deaf person) by its ringing whilst he was reading the signals of the needle. The nuisance is prevented by what is termed joining over or making the short circuit—in fact, by providing for the current a shorter and much more capacious road to the needle coil than by going through that of the bell-magnet, which is made with very fine wire; and the control of the short circuit is put in the hands of the clerk.