We will now tell you a very curious fact about the return of the current. The return icirc is not necessary, nor is it nowr put in practice; for a man named Stern-heil proved, in 1837, that if we buried deep in the ground the end of the wire, attaching it to a plate of metal, the earth itself would conduct the current back again, thus saving the cost of a return wire. Thus, in the figure above, we have represented this by dotted lines, and marked the direction of the return current by double arrows, No being the plates of metal, and having; the wires attached to them.

Electric Telegraph Continued 16

Fig. 7.

"We will now explain the instrument by which communication is made with the battery, and which is qualified not only to send, but also to receive signals. It is represented by Figs. 7 and 8; Fig. 7 being the exterior, and Fig. 8 the interior. The needles in Fig. 7 (for there are usually two) are on the same axis as the, ones on which the electric current acts, only their poles are reversed. - the north pole of the one being opposite the south pole of the other, by which the effect of the earth's magnetism is annulled, and they are the more powerfully influenced by the electric current. It is by means of these outer needles that the signals arc read : they are prevented from deflecting too far from their vertical or upright position by two ivory studs, one on each side; and thus the signalling is rendered more certain and rapid than if they were allowed to oscillate further. The handles at the lower part of the instrument are for moving the barrel in the interior, the one at the side for ringing a signal bell, which is also effected by electricity.

Electric Telegraph Continued 17

Fig. 8.

In Figure 8, we are looking at the back of the instrument, the case being removed. B is the coil of wire for passing a current of electricity round a magnetic needle suspended in it by its axis. In the former drawing, the wire passes but once round the needle ; but by winding it round several times, as here shown, the effect is greatly increased. W, W, are the wires which transmit the current to and from the distant station. We will now see, first, how the instrument is calculated to receive signals. C is a cylinder of box-wood, capped at each end with brass; D, F, H, 0, are slips of metal, the shape of which is seen clearly on the left side of the barrel; a piece of wood. K, projects from the front of the case, having a metal bar, about an inch in length, inserted through the end, standing across it, as in the figure. Now, if W, W", are connected at the distant station with the two poles of a battery, a current will pass along one of these wires, W, and along the slip of metal, 0, to the coil, B, having, in its passage round this, deflected the needle, thereby making a signal; it will descend by a, down the slip of metal, x. thence to the spring, e (which is a part of the same Blip), through the metal bar to e, and thence by F to W", and to the other pole of the battery. We have told you that this return wire, W", is not used in practice: nor is it; but by supposing it to exist here, the direction of the current is more easily understood. We have, by the dotted lines, shown the buried plate attached to this wire. You should look well at the figure, and read this description of receiving signals several times, till you see it clearly ; for though at first sight, the apparatus appears very complicated, it is not so ; these slips of brass, so curiously shaped, being all that is required to receive signals; to send them, the cylinder C is added, the action of which we will now explain. The furthest end of it is joined to one of the handles seen in Fig. 7, by which it is made to revolve in either direction. Supposing, then, we move this handle so as to cause the small metal pin z to press against the spring e, we can thus remove the end of this spring from the short bar against which it rested, whilst the pin y at the other end of the cylinder will touch the curved end of the slip F (both these pins are fixed into the metal caps at the ends of the cylinder). The current will now pass from the battery by the spring H to the brass cap of the cylinder, thence by the pin z to e; e being removed from the short bar, and the current thus cut off in that direction, it will pass to x, which is a part of the same slip as e, thence round the coil deflecting the needle, and passing to the next station by the slip o, and wire W, will deflect the needle there, and return by the earth-current to W". Although it is a crooked path, the electric current traverses it so quickly that no perceptible time elapses between the movement of the needle at our own instrument and the various needles of all the telegraphs on the line. Each handle has a separate cylinder, and each needle a separate coil. one only being represented for the sake of clearness. Every word of the message sent is spelt letter by letter, according to (he num-ber of times that each needle moves. The following is one of the usual alphabets, and (as in Fig. 7) this is commonly inscribed on the instrument. It is the code of a single needle : A - One movement to the left.

B-Two left.

C- Three left.

D - Four left.

E - One left, one right.

F - One left, two right.

G - One left, three right.

H - Two left, one right.

I - Two left, two right.

J - Two left, three right.

K - Three left, one right

L - Three left, two right.

M - Four left, one right.

N - One right.

O - Two right.

F - Three right.

Q - Four right,

R - One right, one left.

S - Two right, one left

T - Three right, one left.

U - One right, two left.

V - Two right, two left.

W - Three right, two left.

X - One right, three left.

Y - Two right, three left,

Z - One right, four left.

With two needles the alphabet is somewhat different; hut you will now understand how the movement of the needles can signify words; and we think you must now have a very good idea of the machinery of an electric telegraph. We shall now show you how the alarum is rung by electricity, to give the clerk at the instrument notice that a message is about to be sent to Lim, that he may be at his post, and ready to watch the needles, and read.

Wonderful as it may appear, an electric current passing round a piece of soft iron will instantly convert it into a magnet; hut its magnetic properties cease as soon as the current stops. In the telegraph alarum this effect of electricity is thus applied : - A is a piece of soft iron, bent into the form of a horse-shoe ; some covered copper wire is wound round it, the ends, B and C, being left loose for the purpose of connecting them with the battery. I) is a piece of steel, connected with the lever, E; the other end of which forms a detent or catch, which falls into one of the notches in the wheel, F. This wheel, when the, catch is removed, will revolve by a spring, and, like the movement in a common clock, acts on the hammer, II, which strikes the bell, (G. B and C are connected with the distant station by a wire, as the needle apparatus. When the operator, therefore, at that station sends a current from his battery along this wire, A will become a magnet, and attract the keeper, D, this, by means of the levers, will release the wheel, F, and the clock-work will cause the hammer to strike the bell. This will call the attention of the operator, who will return the signal and watch the movement of the needles, read the message, and send the reply in the same manner.

Electric Telegraph Continued 18

Fig. 9.