side is connected to the left side of the coil (2) at Peterborough, and its right wire to the left of (3), and its right to to the left wire of (4) at Edinburgh, and then the right wire of (4) carried back to the right side of the London battery, and connected with the zinc plate, or, as we said before, merely attached to a zinc plate sunk in the earth, the current is complete, and when it turns the needle at (1) to the right, it turns them all (2, 3, 4), as

in the figure, precisely in the same direction. On reversing the current all these pointers will turn to the left. If the batteries at intermediate stations were all kept in constant connection with the wires, the needles

along the whole line would always point in one direction and communication be stopped. By a very simple mechanical contrivance, each battery can be connected or disconnected with the main wires when required.

But we must now close up the clock face and study it more closely. I will take the one now in general use in the Post Offices. This face has not really a clock-face dial but the letters of the alphabet are painted upon it in regular order, half on each side, as in the accompanying figure 7.

The handle is used to connect or disconnect the wire of the coil and the battery. By working it to the left the current is sent one way, and by working it to the right it is reversed,-i.e., sent in the opposite direction: and the electricity running through the coil moves the needle to the right or left; when disconnected, the needle stands upright.

Now, look at the face of the apparatus (fig. 7.). To the left is the letter A, with one short line under it slanting towards the left, one long line slanting to the right. To telegraph the letter A, then, the needle must be moved so as to send the current once in each direction; the first movement will cause the needle to point to the left, the second to the right. So with letter B, the needle must be pointed once to the right and thrice to the left. Let us take the word "face". we must make the needle go twice to the left, once to the right and once to the left for F; once to the left, once to the right for A; twice to the right and once to the left for C; once to the left for E. Then the clock will stop, and the needle will stand upright, because it is disconnected, and the receiver will understand that a word is finished, and if he understands it, he telegraphs one beat to the right: if he does not, he telegraphs to the left and the word is repeated. So each word in a message is spelt out, letter by letter; and, where great accuracy is required, the whole message is telegraphed back by the receiver to the sender, to make sure that he has understood it correctly. This is often desirable, as in telegraphing quickly two letters may

follow one another so rapidly, that they may appear to the receiver to be only one letter; thus, CE might be received as Z: but mistakes are sometimes made by the clerk receiving the message at the instrument reading off each word, as it is transmitted, to another, who writes it down from his dictation. An instance of this occurred not long ago, where the head of a large brewing firm telegraphed to his wife-"I am brewing to-day, and cannot come home to-night." The clerk who wrote this message down from the receiver misunderstood the word brewing, and wrote—“ I am ruined to-day, and cannot come home to-night." On receipt of this intelligence the distracted wife hired a post-chaise and posted off some thirty miles to the brewery, where, on arriving in the middle of the night, she found her unconscious husband in his shirt-sleeves presiding over the mashtub.

As messages to a foreign country are more liable to mistakes, from the clerks misunderstanding the language, a printing apparatus is attached to the instru ments, which, according to the working of the needle, stamps each letter on a strip of paper at both instruments, and this is cut into words and pasted upon a message form and delivered to the person to whom it is addressed.

In calling attention to any office to which the clerk wants to send a message, he telegraphs two letters marked on what is called a code of signals, pasted up by the side of the instrument, which signals represent the office he is calling. These letters are generally either the first and last letters of the name of the town, or the first and most peculiar letter in the name: thus, OX stands for Oxford. He keeps on telegraphing OX, until the clerk at Oxford moves his needle one stroke to shew he is attending, when the sender of a message telegraphs the signal of the office at which he is stationed, and then begins his message.

It will be noticed, that on the dial all the long strokes denote movements of the needle to the right, and all

short ones movements to the left. They are thus written in the book of instructions:

A telegraph clerk has lately discovered, that by twisting the coils of wires that unite the needle to the battery, it is possible to transmit two messages with the same instrument in the two opposite directions of the same wire, e.g., both to London and Edinburgh.— Rev. J. Ridgway.

THE BODY AND ITS PARTS.

THE bones of the human body (including the teeth) are 255 in number, and are so united as to combine the greatest strength with the most perfect freedom of motion. How is it that these parts are held together in constant action, for 60 or 70 years without wearing out? The body is capable of existing and moving for even 100 years, during which its parts are constantly worn out and restored, so that about every seven years all the old materials are entirely gone and new ones put in their place. How is this waste supplied, and the worn-out

substance restcred? How is it that action, which destroys most things, only strengthens the human body? You know that any machine, if it is always running, wears out, and wants a new wheel here and a new rivet or spindle there, and we say "it is worn away;" but the more you work your arm or your leg, the bigger and stronger the muscles of the arm or leg become.

Before we answer these questions, it is necessary to know a little about the structure of the body, which consists of three great parts, viz.: the head, trunk, and limbs.

1. The head surmounts the fabric, and is a sort of ball, formed mainly of plates of bone, so arranged and fitted together as to unite the greatest possible strength with the greatest possible lightness. The interior of the skull (which consists of eight bones) is entirely

Fig. 1.

filled with brain, which is the root of all sensation and life. It is the centre in which all the senses meet, through which the brain gets all its ideas.