Our limits will not permit us, nor indeed is this the proper place, to give an account of the fine discoveries of Arago and Faraday, on the magnetic properties of electric currents. MM. Arago and Ampere magnetized needles instantaneously by placing them within a helix of insulated copper wire, so that the electric current passed in a direction perpendicular to their length. Mr. Sturgeon of Woolwich applied this principle to the construction of temporary magnets of great power by merely surrounding soft iron, either in the form of bars or of a horse shoe, with insulated coiled wire. The soft iron becomes a powerful magnet while the electric current is passing through the coil, and loses its power the moment the current is stopped. In this way Mr. Joseph Henry, now the distinguished Secretary to the Smithsonian Institution, produced magnets which were capable of lifting several tons, and the same principle has been employed by Logeman and others for communicating permanent magnetism to steel.

Mr. Faraday's beautiful discovery of electro-dynamic induction in 1832, was a most important step in the improvement of the electric telegraph. He demonstrated by two fine experiments, that an electric current is capable of developing at a distance by induction electric currents in a conducting wire. If we suddenly bring near to any part of a conductor forming a closed circuit another conductor traversed by a current, we produce instantaneously on the first conductor a current moving in a direction contrary to that of the inducing current, or that brought near the conductor, and when we reverse the inducing current we produce instantaneously in the first conductor a second current moving in the same direction as the current that is reversed. Mr. Faraday also found that a magnet is capable of inducing similar currents in a conducting wire, and that the phenomena of induction may be produced in the conducting wire itself, an effect which is termed the induction of a current upon itself. Mr. Faraday was thus led to the construction of a magneto-electric machine which was greatly improved by Pixii, Saxton, and Clarke, and extensively employed for telegraphic purposes.

Such is a brief notice of the history of the electric telegraph, and of the principal discoveries in electricity and magnetism, upon which the present telegraphic apparatus is founded. It is not our intention to give any

more or less ingenious, by which telegraphic communications are generally transmitted. It is difficult for ordinary readers to understand these operations even with the aid of good diagrams,* and those who are desirous of making themselves master of the apparatus commonly employed, will do this most satisfactorily by visiting any of the stations where an electric telegraph is placed. Our object in the present article is to give some account of the general telegraphic system, and of the labors and services of those who have been the means of introducing the electric telegraph on our railways, and who have invented remarkable contrivances for communicating intelligence, such as the printing telegraph, the electro-chemical telegraph, the autographic telegraph, and any others that are distinguished from those commonly used by remarkable peculiarities.

We have already seen from the experiments of Sir W. Watson, and the fact was evident from every future experiment, that the electric power was transmitted along wires instantaneously, or in so short a time that its velocity could not be appreciated by the ordinary instruments by which time is measured. Any more accurate measure of its velocity was of no consequence for telegraphic purposes. Means, however, have been taken to obtain a rude estimate of its velocity, which of course must depend on the conducting power of the transmitting wire, though it does not upon its thickness. By a very ingenious apparatus Mr. Wheatstone found that the electric force moved along a copper wire at the rate of 288,000 miles in a second. According to the more recent experiments of MM. Fizeau and Gonelli its velocity is only 112,680, less than half of the preceding estimate. In the iron wire employed for telegraphic purposes, its velocity, according to MM. Fizeau and Gonelli, is only 62,000 miles in a second; according to Professor Mitchell of Cincinnati 28,500; and according to Professor Walker of the United States, 16,000 miles. But it is obvious, that whichsoever of these velocities is the correct one, the electric influence is transmitted in so short a time that an effect produced at one station is produced simultaneously with the effect produced at another.

In order to transmit messages along the

*The reader will find the most complete and inDr. Lardner's admirable chapter on the subject, in telligible description of telegraphic apparatus in the third and fourth volumes of his Museum of Science and Art.

poses are commonly made of iron about the sixth part of an inch in diameter. They are coated with a plating of zinc, by what is called galvanization. As zinc is very oxydable, it is soon converted by the air and by moisture into an oxyde of zinc, which being insoluble in water, protects the wire from rust and corrosion. M. Haighton, however, has found that the gases from the smoke of large towns converts the oxide into a sulphate, which being soluble in water permits the wire to be corroded, and to such a degree that he found his wires reduced to the dimensions of a common sewing needle in less than two years. Some very peculiar conditions of the wires in America, which are not galvanized, have been discovered. On the telegraphic lines which cross the extensive prairies of the Missouri, the telegraphs refuse to act in the months of July and August during the four hottest hours of the day, from 2 to 6 o'clock! Many inferior contrivances, which require diagrams to make intelligible, and which will be found clearly described in Dr. Lardner's volumes, have been adopted to insulate the wires in passing the posts. The wires at the posts generally pass through tubes of earthenware or of glass, or they rest upon cylinders or rollers of the same substance. In order to prevent the bending of the wires, and their mutual interference in high winds, an apparatus is placed at distances of half a mile for tightening them, and the posts where this is done, and which are larger than the usual ones, are called winding posts.*

We have already stated that the electricity of the aurora, comparatively feeble as it is, deranges the operation of the telegraph; but the influence of atmospheric electricity in thunder-storms is of course much more injurious, and is often dangerous at telegraphic stations. The natural remedy for this is to place conductors on the top of each post, which is very easily done; but at telegraphic stations very beautiful and efficacious contrivances for their protection have been invented by Mr. Walker of the South-Eastern Company and M. Breguet of Paris. A remarkably fine copper wire is placed between the main wire and the station, so that any current of electricity imparted to the main wire must pass through the fine one before it reaches the station: but the effect of powerful electricity upon a fine wire is to fuse or deflagrate it, owing to the difficulty that it has in passing along so narrow a channel; so that

If we place our ear close to one of these posts during a breeze, sounds like those of falling water are distinctly heard.

all communication between the wire of the station is cut off by the destruction of the fine wire. Cases have occurred in which these wires have | been made red hot, and even melted.

When the system of wires is thus erected either above or below the ground, it becomes interesting to see at what rate signals or words can be transmitted to great distances. About three years ago some interesting experiments on this point were made in Paris by M. Leverrier and Dr. Lardner before committees of the Institute and the National Assembly. In one experiment, a message of 40 words was sent 168 miles, and an answer of 35 words returned, in the space of 4 minutes and 30 seconds. In another experiment, a message of 282 words was transmitted along a continuous wire 1,082 miles long. "A pen," says Dr. Lardner, "attached to the other end, immediately began to write the message on a sheet of paper moved under it by a simple mechanism, and the entire message was written in full in presence of the Committee, each word being spelled completely and without abridgment, in fiftytwo seconds, being at the average rate of five words and four-tenths per second!" This was done by Mr. Bain's electro-chemical telegraph, which the writer of this article saw in operation at the time when this experiment was made in Paris, and which, from its peculiarly ingenious construction, we shall endeavor to describe.

The sheet of paper which is to receive the written message is wetted with an acidulated solution of the ferroprussiate of potash, and placed upon a plate of metal. If we now take a metallic point or style, and place it in contact with the paper, and conceive a current of electricity to pass through the style, it would enter the copper plate through the paper and make a blue spot, so that we could easily write upon the paper, as if blue ink streamed from the point of the style. Let us now suppose that the upper end of the style is connected by a wire with the positive pole of a voltaic battery, and the metallic plate with the negative pole, a current will flow through the point of the style whenever it is brought in contact with the paper, and will decompose the prussiate of potash, one of the elements of which will mark it with a dark blue spot. If the paper is moved or drawn aside, the style will trace a blue line upon it. If the current is stopped at different intervals, the blue line will be stopped also, and we blue lines, in proportion to the length of time shall have short or long spaces between the during which the current has been stopped.

Mr. Bain has contrived various ways of | moving the paper beneath the style, but the one which he prefers is to lay a large circular disc of it upon a metallic plate of the same size, which is made to revolve by clock-work round its own centre and in its own plane, while the style has a slow motion from the centre to the edge of the disc. The consequence of these two movements is, that the style will describe a spiral commencing at the centre of the disc of paper, and terminating at its edge; and when the current passes through the circuit uninterruptedly, this spiral will be a continuous blue line, but if the current is interrupted, it will consist of short blue lines and white spaces of different lengths.

The next step is to construct an alphabet for this telegraph, which is done as follows:The letter a is represented with one short line thus b with one long and two short lines, c - with the same lines differently placed, d with four lines e with two short ones -, f with two long ones, and so on, the greatest number for any letter being four lines, with short and long ones differently placed.

The message being supposed to be written out, a narrow ribbon of paper, about half an inch wide, after being unrolled from a cylinder, is made to pass between rollers under a punch, which by an ingenious mechanism punches out a hole beneath it, and through the paper when it is passing. Two or three of these holes form the short line a -, and several form the long lines, such as f

The operator is thus able to make short or long lines at pleasure, and can therefore perforate in the paper-ribbon or messagestrip the message which is to be sent. In this work a number of agents may be simultaneously employed in perforating messages for the telegraph, to which they are applied in the following manner :

The perforated message-strip is now coiled upon a roller, and placed on an axle attached to the telegraphic machinery. The extremity where the message commences is then placed on a metallic roller in connection with the positive pole of the voltaic battery, and is pressed upon the roller by a small metallic spring terminating in points like the teeth of a comb This spring communicates with the conducting wire, and when it falls into the perforation of the paper, the electric current passes to the point of the recording style, which then makes a blue line corresponding to the one in the perforated stripe, but when the spring rests upon the white paper be

tween the perforations, the electric current does not pass, and the style makes no blue mark, but leaves a corresponding blank. In this way the message of perforation is transferred in blue lines to the chemical paper a thousand miles off, and arranged in a spiral from the centre to the circumference of the paper disc. A boy previously taught reads this record to a clerk as quickly as if it were in ordinary type.

The reader can not fail to be struck with the singular beauty and ingenuity of this contrivance, imperfect as our description of it must be. When we saw in Paris the whole operation of perforating the message, and recording it in blue lines at the other end of the wire, it seemed more like magic than any result of mechanism which we have ever seen. The dry steel point, when tracing its spiral path, actually seems to be depositing blue ink upon the paper. But it is not merely ingenuity that is the characteristic of Mr. Bain's Telegraph. In is unlimited in its quickness, and unerring in its accuracy; and it has another advantage of requiring a battery of much less power than other forms of the telegraph. An example of the value of its accuracy was recently shown in a case where the importance of a single figure was experienced. In an agitated state of the funds, a stock-broker in London received from a distance an order to purchase at a certain time of the day, £80,000 of consols. The broker doubted the accuracy of the number from the magnitude of the sum, and as the message had been sent by the recording instrument, it was found that the real message was to purchase only £8000 of consols, the transcriber having by mistake inserted a cipher too many.

But this telegraph has another advantage which no other possesses. It is a cipher telegraph, by which individuals may communicate with their friends, or companies with their correspondents, or governments with their distant functionaries. The short and long lines of the telegraphic alphabet may be varied in innumerable ways, which it would be impossible to decipher, and a punching machine, which would cost little, might be either in the possession of individuals, or at their command in the town or village where they reside. Any arrangement of this kind, however, is not likely to be adopted, except in a small number of cases, until the expense of telegraphic despatches is reduced to a very moderate sum. But if such a change should take place analogous to the penny-post, as Dr. Lardner has stated, Mr. Bain's telegraph