and the latter by closing it for a longer time, by means of the key. The signs are received at the distant station by the corresponding attractions of the armature of an electromagnet, which marks them on a strip of paper in its vicinity. The plan by which these arrangements are made at two stations is represented in Fig. 24. At each of the stations, B is a battery of voltaic pairs, connected between the point 1, underneath the metallic lever K, and the earth. When the lever K is not being manipulated, it is held by a spring upon the metal point 2, between which and the earth are inserted the coils of the electro-magnet м, whose armature is employed to mark the paper and record the signals given from the distant station. On pressing down the key K, for

example, the contact between the lever and the point 2 is interrupted, and that at 1 established, the current of the battery в goes from a through the contact point 1, and front part of the lever to 3, where it enters the line L. Arriving by L', the current passes over K, from the middle 3, to the

back contact point 2, and from this, the key being at rest, it traverses the coils of the electro-magnet M', and then goes through the earth back again to the battery B.

55. Simple Morse Embosser for two Stations with Relay.— When the line connecting two stations is long it is impossible sometimes, even with very great battery power, to move the armature of the electro-magnet with force enough to impress the paper legibly. It was on this account that Morse employed a relay to work his recording apparatus. Fig. 25 represents a plan of connection of a Morse embosser with relays and local batteries for two stations. G is the line galvanoscope connected, on the one side, with the line, on the other, with the lever of the key K. Its purpose is to show the presence of current in the line, and to give a rough idea of its strength. The front or working contact 1 of the key is connected with the pole, c, of the line battery B, and the other pole, z, with the earth-plate. The back, or reposing contact, of the key is connected with one end of the electromagnet coils of the relay R, the other end being in communication with the earth-plate. Lastly, between the contactpoint 2 of the relay and its tongue or armature are inserted the coils of the Morse м and the local battery L B.

When in repose the levers of both keys are on the contacts 2, and the line, therefore, at both ends to earth through the coils of the relays. On pressing down either of the keys the current passes direct from the z-pole of the battery to the earth-plate and earth, and from the c-pole through the line galvanoscope, line, key of opposite station, and relay to earth. The deflection of the relay-tongue from contact 1 to contact 2 closes the local circuit, and the armature of the receiving instrument works in conformity with the motions of the key at the sending station.

56. Another method of connecting up the same instrument for two stations is shown in Fig. 26. In this method the lever of the key is in permanent contact with earth. The c-pole of the battery is connected with the front contact of

the key, and the z-pole with the point of junction between the galvanoscope and relay, the latter being inserted between the galvanoscope and back contact of K. The local circuit is arranged as before.

A current arriving by the line while the key is at rest passes through the galvanoscope, coils of relay, back contact and lever of key, to earth. When the key is pressed down on the contact 1, the c-pole of the battery is put to earth through the lever of the key, and the circuit being thus completed, the current from the z-pole passes through the galvanoscope into the line.

In the former method (Fig. 25) the operation of the key

consists in shifting the line from relay to battery. In the other method, the battery and relay have the same fixed contacts 1 and 2 of the key; but the earth and line change places, the line taking the place of the earth in the former, and the earth being shifted by the key from relay to battery.

This is by no means so good as the former method, because it necessitates a good insulation of the battery, without which a current, depending on the magnitude of the

fault, will not only pass always through the line, but also through the coils of the home-relay; and any accidental contact of the battery with earth will give a signal at the relays of both stations; whilst, with the former method, a similar accident would be entirely without effect further than weakening the currents sent on to the line, notice of which is amply given by the galvanoscope.

57. The Morse Code. The elementary signs of the Morse telegraph are two, a dot and a dash, produced by the recording instrument according to the time which the key at the transmitting station is held down.

The general adoption of this system on the Continent some years back occasioned the establishment of certain rules for the settlement of the letters, numerals, &c., which have been subsequently almost universally adopted.

The formation of so many letters, &c., out of two elementary signs required the greatest number of variations with the given number of elements.

The number of variations, with repetitions of two elements, are:

Therefore, by using variations of from one to four of the two elementary signs, we have at our command

variations for the formation of an alphabet.

These variations, with some others, have been disposed as follows: