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Interesting Particulars Concerning the Magnet: Reiss

As far as attempts to transmit sounds are concerned, the telephone cannot be looked upon as a new instrument. Many years ago, Professor Page found that an electro-magnet gave a kind of click or snapping noise at the moment when the current was passed through its coil. Philip Reiss, of Germany, in 1861, took advantage of this discovery in the construction of what may be called the first telephone. It consisted of a box, containing a mouthpiece through which the operator could sing. At the upper part of the box was an orifice closed in with a diaphragm of parchment. This parchment had in its centre a metallic disc, which all but touched a platinum wire fixed above it. When the diaphragm was thrown into vibration by the singer's voice, the disc was caused with every vibration to touch the platinum point above it. As the disc and wire were in circuit with a battery, these touches, following one another at the rate of some hundred per second, formed electrical contacts which were telegraphed to an electro-magnet at the distant station. Here they were translated into a series of clicks on Professor Page's system, and as these clicks necessarily followed one another with periodic regularity, they were, by a well-known acoustical law, converted into musical sounds. Such a sound depends for its pitch on the number of vibrations which it possesses per second, and as the operator in this case had the means of causing the electrical contacts to agree in number with the vibrations of his voice, it follows that the same sounds were reproduced.

Another form of telephone which followed this was the contrivance of Mr. Elisha Gray, of Chicago. It consisted of a number of metal reeds actuated by electro-magnets, and, like that of Reiss, was only capable of transmitting musical sounds. The honour of having been the first to demonstrate the possibility of transmitting articulate speech by telephone belongs to Professor Graham Bell. The instrument which he devised is so simple in its character that any boy with clever fingers can easily make one. And as I am quite sure that most of my readers would like to have the means of using such an interesting piece of apparatus, I will presently give full directions, which will render the matter quite easy.

The action of the magnetic telephone can be better understood if we consider the peculiar but invisible force which surrounds the poles of a magnet. We may get some idea of this force by a little experiment, the results of which are both astonishing and pleasing. Take any magnet and lay it upon the table with a piece of stiff card above it. Now sprinkle the card with some iron filings sifted through a piece of muslin. Tap the card with the finger-nail, and immediately the filings arrange themselves in beautiful curved figures, exhibiting what are called the curves of magnetic force. Here then is this strange power made evident to our senses. We may be certain that any piece of iron introduced within this magnetic field must have a tendency to vary its conditions, and this is what is done in the telephone. It consists of a bar magnet, four inches long, and a quarter of an inch in diameter. The end of this bar is capped by a little reel, which may be made either of wood or cardboard. This reel is wound with silk-covered copper wire (No.36), and about half an ounce will be required for the purpose. A small hole should be drilled in one side of the reel close to the magnet, through which the end of the wire must be passed before the winding is commenced. The winding must then be carefully done, layer by layer, until the reel is quite full, when the free end can be made fast by passing it beneath the last two or three layers. A wooden holder, which is shown in the annexed cuts in elevation and section, will be required as a case for the telephone. This can easily be turned out of a dry piece of mahogany by any one who possesses a lathe. In any case a professional turner would make it for a very small sum. It will be noticed that it is in two distinct parts, which are afterwards screwed together. One part forms a kind of cup and stem for the reception of the reel and magnet. The outer opening of the cup has a little recess cut out of it for the reception of a thin plate of iron which should be cut out of the metal plate upon which ferrotype photographs are taken. In the absence of this, a piece of thin tinned iron will answer the purpose.

The next illustration is a section of the completed instrument which will afford sufficient guide in putting the various parts together. M is the magnet, A the coil, D the mouthpiece, B B terminal screws to which the two ends of the coil wire are respectively carried. C a screw for adjusting the magnet to a position as close as possible to the iron diaphragm without actually touching it. This iron diaphragm fits into the recess already pointed out, and completely closes the cup. Its surface is seen inside the orifice of the mouthpiece when the instrument is complete. In purchasing materials it must be remembered that two of each thing will be required, for two instruments must be constructed, one for each end of the line-wires. These wires are fastened to the screws B B, which are placed outside the instrument for that purpose. In making the connection between these screws and the ends of the coil, the latter must be stripped so that the contact is metallic. The join can best be effected with a soldering iron; but if this operation is beyond the powers of the worker, he can first pull the wire through the hole, and then turn the screw in by its side. With a pair of such simple instruments as these, speech can be conveyed for very many miles, each instrument acting as transmitter and receiver, as it is placed either to the mouth or the ear. Let us now consider the means by which this telephone--which requires no battery current--is enabled to give these astonishing results. In the first place, we have a magnet placed within a coil of wire. Remembering Faraday's experiments in this direction, which have already been detailed, we shall know that an electric current can be generated in the wire by this means. In front of the coil is a flexible plate of iron which is caused to vibrate with every sound uttered in its vicinity. This plate is therefore caused to move to a slight extent, by these vibrations, from and towards the coil. This movement, slight as it is, is sufficient to vary the condition of the magnetic field. Such variations are carried along the line-wires until they reach the distant telephone. Here they cause similar variations and the diaphragm of the distant telephone is alternately repulsed and attracted in the same manner, and its vibrations give out the sounds as originally uttered. Such is the theory by which the action of Bell's magnetic telephone is explained. The telephone as originally constructed--of which the one here described is a modification to suit the powers of young workers--is capable only of giving very feeble results; but if the various parts be carefully adjusted, and particular attention be given to the distance of the magnet from the diaphragm (this can be easily arrived at by experimental trials), the articulation is remarkably clear and distinct. The instrument has lately been much improved by Mr. F. A. Gower, who has entirely altered its form. The magnet is no longer a bar, but is of the shape of the letter D, its two poles being turned upwards and each inclosed in a coil. These magnets are made abroad, and are so powerful that they will each lift a weight of about twelve pounds. The telephone in its improved form is coming into commercial use both in London and other cities. Its great objection seems to lie in its extreme sensitiveness, for it will often transmit messages which are not intended for it, and which are being transmitted through lines near those with which it is connected. This strange phenomenon is due to the fact that an electric current passing through a wire will induce a current in a neighbouring wire.