gested, or which have been practically developed, through various combinations of the elements involved in these systems. But there has been another claimant for public favor, of which brief mention has already been made, whose fundamental principle is older than the needle or the electro-magnet. It is that in which the registration of the message is accomplished by means of chemical decomposition. Experiments upon this method were made at an early day, in which as many wires were used as there are letters of the alphabet: each wire led to a small cup or tube containing water, into which was plunged the extremity of the "return wire," one of which would serve for all of the "leading" wires. Each tube was marked with a letter, and, when it was desired to signal any particular letter, it could be done by closing the circuit through the proper tube, thus causing bubbles of gas to appear. This was essentially the system of Sommering of Munich, who constructed a model in 1809. A curious and ingenious feature of his method was a device for the setting of an alarm so that the operator might be relieved from the necessity of constantly watching the glass tubes. It consisted of a sort of lever, on the long arm of which was a small inverted bowl, covering the open end of one of the tubes in which gas was

evolved. On the short end was a small metal ball, free to roll off when the lever was slightly tipped. If the operator at the distant end wished to open communication, he closed this particular circuit for a minute or two, during which time gas was generated. This collected in the inverted bowl, and, in virtue of the upward pressure of the gas, the lever was tipped, the ball would drop, and the alarm was set off.

The first realization of a practical system of telegraphy based on electro-decomposition was by Alexander Bain of Edinburgh. He took advantage of the fact that many salts are decomposed with the utmost facility by electricity, and by extremely feeble currents, and that this decomposition can be rendered evident through a recomposition, in which colored compounds are produced. If a little iodide of potassium be dissolved in water, and a little starch paste be added, the mixture will show a blue color about the positive pole when a very feeble current is passed through it. If any kind of porous paper be soaked in this liquid, and placed on a metallic plate connected with the negative pole of a battery, a blue mark will be made upon it wherever touched by the positive. pole. From this the essence of Bain's invention will be readily understood. Imagine the paper to have a uniform movement over the

metal plate, and a metal style connected with the line-wire to rest upon its upper surface. As long as no current is passing, no mark will be made; but, when the key is closed at the other end of the line, the style leaves a blue trail as the paper passes under it. It is only necessary to adopt an alphabet of long and short marks, or "dots and dashes," to complete the device. Bain's system was patented in England in 1846, and was introduced into this country in 1849. A number of lines working the system were erected, some of them of great length, and the Bain telegraph was at once successful and popular. After a few years, however, it was displaced by the Morse system. It is in most respects the simplest of all telegraph systems; and, in spite of its early rejection, it possesses decided merits, among which are the ease with which it can be adapted to rapid automatic telegraphy, and its ready application to autographic transmission. Further developments will be required to enable it to compete successfully with its long victorious rival.

The better-known effects of electricity are as follows: Electro-static attraction and repulsion, heating effects, chemical decomposition, electromagnetic effects, physiological effects. Ronalds and the older electricians relied upon the first of these as a means of producing signals at a

distant point. Among the numerous efforts to avoid interference with the Morse patent was a telegraph system in which the second was utilized. The current was made to pass through a short piece of thin platinum wire, which, becoming red-hot, burned holes, long or short, in a moving strip of paper. Sommering, Bain, and others, have utilized the third; Schilling, Gauss, Steinheil, Wheatstone, Morse, and many others have depended upon the fourth; while experiment, and occasionally necessity, has demonstrated the possibility of making use of the fifth. It has also been proposed to use other, more obscure effects of electricity for telegraphic purposes; but the telegraph of to-day is the electro-magnetic telegraph. Practically, all other systems have been abandoned for this. No attempt can be made here to describe the numerous, and in many instances wonderful, modifications and improvements which have been ingrafted upon the original stem, involving devices for rapid and automatic transmission, machines for printing the message in Roman characters as fast as received, instruments for repeating the message from one line to another, etc. Two or three extensions of original methods, which involve new principles or espe cially novel features, will be briefly considered in the following chapter.

CHAPTER V.

MULTIPLEX TELEGRAPHY AND SUBMARINE

CABLES.

THE rapid growth of the electric telegraph during the decade from 1840 to 1850, and its marvellous performance, justly excited the curiosity and challenged the admiration of all intelligent people. Within a few years after its first introduction, it grew to be an important factor in business and social life, and many understood something of the philosophy of its operation. Few, however, were at first willing to give credit to certain suggestions as to further possibilities of its improvement, and this was particularly true when it was asserted to be possible to transmit simultaneously two messages in opposite directions over the same wire. Although this has now become an all but universal practice on lines doing a large amount of business, it is not too much to say that, to the great majority of the uninitiated, the operation is still a mystery; and this in spite of the fact that the principles involved are extremely simple.

H