Pagina-afbeeldingen
PDF
ePub

indebted in this country for all the advan- | account of the innumerable inventions, all tages of telegraphic communication.

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 be-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.

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 comes 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.

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

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

|

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.

|

telegraphic wires, a certain amount of electric power is required, and this force must be increased in proportion to the length of the wire. A large wire, however, will transmit more electricity than a small one, in proportion to the squares of their diameters, or the areas of their section. According to some accurate experiments made by M. Pouillet, a distinguished member of the Institute of France, a voltaic battery of ten pairs of plates will supply electricity sufficient for telegraphic purposes by means of a copper wire one-eighth of an inch in diameter, and 600 miles in length. A force of much less intensity, however, is amply sufficient, as it is easy to strengthen the current by batteries at intermediate stations.

Having obtained a cheap and durable line for conducting the electric influence, and a simple power for generating it of sufficient intensity, the next step is to place the lines or wires in a proper position. The general practice has been to support them by posts placed at the distance of sixty yards. On some lines the distance of the posts is much greater; and on the great telegraphic line between Turin and Genoa, the wires are carried across extensive ravines and valleys, from half a mile to three quarters of a mile in width, without any support whatever, and at an enormous height above the ground. When the line reaches Turin it passes under ground, and when it arrives at the Maritime Alps it stretches from crest to crest, hiding itself again in the earth till it terminates at the ducal palace in Genoa.

being injured by human hands. M. Siemens has observed two interesting facts on these lines. In the one a diminution of the effect is produced by inverse currents arising from the wires acting like a Leyden phial. The gutta percha which coats the wire is the glass of the phial, the wire is the internal coating of the phial, and the damp ground is the external coating, so that the opposite electricity of the ground acts upon, and neutralizes to a certain extent the internal electricity of the wire. It was apprehended that this disturbing cause would have interfered with the working of the subterranean wires, but the Magneto-Electric Telegraph Company, who have in work 900 miles of subterranean wire, and who often send their messages through 500 miles without any stoppage, have not experienced any inconvenience from it. The other phenomenon observed by M. Siemens is the electrical influence upon the wires by the Aurora-Borealis. During the brilliant display of this phenomenon on the 18th October, 1848, he observed currents varying in intensity and direction, in the line between Berlin and Coethen, 20 German miles in length, the direction of which was E.N.E. to W.S.W., nearly perpendicular to the magnetic meridian. During the prevalence of this meteor, the electric telegraphs in England were temporarily unfitted for use.

In the telegraphic lines established in India by Dr. O'Shaughnessy, he has adopted both the aërial and subterranean system. He found that the wires used in England were quite insufficient in India. In his experimental line of eighty miles from Calcutta, he was obliged to employ iron rods resting on bamboos. Flocks of heavy birds like the adjutant perched upon them, and groups of monkeys followed their example, while loaded elephants broke them down when they came in their way. He therefore used thick galvanized wires suspended at the height of fourteen feet upon posts upwards of 200 yards apart, and so strong was the system, that a soldier suspending himself from the middle of one of these long wires

M. Siemens, whose ingenious telegraph received a Council Medal at the Great Exhibition, and which is used on all the Prussian lines, and those in the north of Germany, recommended the subterranean system of construction, and had it carried into effect on upwards of a thousand miles of German railway. By carefully covering the copper wires, which were about the 50th of an inch in diameter, with gutta percha, to prevent the escape of the electricity, by placing them about 24 feet deep in iron tubes, and by ingenious methods of discovering the locality

of any defect either from the insulating coat-produced on it but a small curvature. In ing or from the copper wire, he found the the subterranean system, where it is used in system answer so well, that at the end of India, Dr. O'Shaughnessy lays at the depth three years the wires had not suffered the of two feet his wires, coated with gutta perslightest change. There are obviously many cha, on wooden sleepers saturated with arseadvantages in the subterranean system. The nic, in order to defend them from the white wires are not influenced by rain or snow- ants, which we suppose, like the rats in the they are secure against storms and hurri- north of Germany, reckon gutta percha a canes, and their locality in the earth, as well great luxury. as upon the railway path, protects them from

The wires employed for telegraphic pur

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 oxyd-| able, 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.

m

Mr. Bain has contrived various ways of tween the perforations, the electric current moving the paper beneath the style, but the does not pass, and the style makes no blue one which he prefers is to lay a large circu- mark, but leaves a corresponding blank. In lar disc of it upon a metallic plate of the this way the message of perforation is transsame size, which is made to revolve by ferred in blue lines to the chemical paper a clock-work round its own centre and in its thousand miles off, and arranged in a spiral own plane, while the style has a slow motion from the centre to the circumference of the from the centre to the edge of the disc. paper disc. A boy previously taught reads The consequence of these two movements is, this record to a clerk as quickly as if it were that the style will describe a spiral com- in ordinary type. mencing at the centre of the disc of paper, The reader can not fail to be struck with and terminating at its edge; and when the the singular beauty and ingenuity of this current passes through the circuit uninter-contrivance, imperfect as our description of ruptedly, this spiral will be a continuous blue it must be. When we saw in Paris the whole line, but if the current is interrupted, it will operation of perforating the message, and reconsist of short blue lines and white spaces cording it in blue lines at the other end of of different lengths.

the wire, it seemed more like magic than The next step is to construct an alphabet l'any result of mechanism which we bave ever for this telegraph, which is done as follows:- seen. The dry steel point, when tracing its The lettera is represented with one short spiral path, actually seems to be depositing line thus -, b - – with one long and blue ink upon the paper.

But it is not two short lines, c

with the same merely ingenuity that is the characteristic of lines differently placed, d with four lines Mr. Bain's Telegraph. In is unlimited in its

é with two short ones --, f quickness, and unerring in its accuracy; and

with two long ones, and so on, the it has another advantage of requiring a greatest number for any letter being four lines, battery of much less power than otber forms with short and long ones differently placed of the telegraph. An example of the value

The message being supposed to be written of its accuracy was recently shown in a case out, a narrow ribbon of paper, about half an where the importance of a single figure was inch wide, after being unrolled from a cylin- experienced. In an agitated state of the der, is made to pass between rollers under a funds, a stock-broker in London received punch, which by an ingenious mechanism from a distance an order to purchase at a punches out a hole beneath it, and through certain time of the day, £80,000 of consols. the paper when it is passing. Two or three The broker doubted the accuracy of the of these holes form the short line a -, and number from the magnitude of the sum, and several form the long lines, such as f as the message had been sent by the record

The operator is thus able to make ing instrument, it was found that the real sbort or long lines at pleasure, and can there- message was to purchase only £8000 of confore perforate in the paper-ribbon or message sols, the transcriber having by mistake instrip the message which is to be sent. In serted a cipher too many. this work a number of agents may be simul- But this telegraph has another advantage taneously employed in perforating messages which no other possesses. It is a cipher for the telegraph, to which they are applied telegraph, by which individuals may commuin the following manner :

nicate with their friends, or companies with The perforated message-strip is now coiled their correspondents, or governments with upon a roller, and placed on an axle attached their distant functionaries. The short and to the telegraphic machinery. The extremity long lines of the telegraphic alphabet may be where the message commences is then placed varied in innumerable ways, which it would on a metallic roller in connection with the be impossible to decipher, and a punching positive pole of the voltaic battery, and is machine, which would cost little, Inight be pressed upon the roller by a small metallic either in the possession of individuals, or at spring terminating in points like the teeth of their command in the town or village where a comb This spring communicates with the they reside. Any arrangement of this kind, conducting wire, and when it falls into the however, is not likely to be adopted, except perforation of the paper, the electric current in a small number of cases, until the expense passes to the point of the recording style, of telegraphic despatches is reduced to a very which then makes a blue line corresponding moderate sum. But if such a change should to the one in the perforated stripe, but when take place analogous to the penny-post, as the spring rests upon the white paper be- | Dr. Lardner has stated, Mr. Bain's telegraph

а

If a

would be the only expedient of all those hitherto contrived by which such augmented demands could be satisfied, the instruments in common use, of whatever form, being utterly inadequate to the purpose. How this would be effected by Mr. Bain's telegraph, Dr. Lardner has satisfactorily shown. Nothing more," he says, "would be necessary than to engage a great number of persons, for the purpose of committing the despatches to the perforated ribbons. great number of despatches, short or long, be brought at once into the telegraphic office for transmission, let them be immediately distributed among a proportionate number of the persons engaged in the preparation of the ribbons. A long despatch might be divided into several portions, and distributed among several, just as a manuscript report, intended for publication in a journal, is distributed among several compositors. When the despatches thus distributed should be committed to the ribbons, new ribbons might be connected together, so as to form longer continuous ribbons, which being put into the telegraphic instruments, would be sent to their destination at the rate of 20,000 words an hour on each wire!"

66

In certain cases, such as the transmission of reports of debates, or speeches of public interest, or Government despatches, the same documents are required to be sent to different places. We have then only to take the perforated ribbons to the different wires belonging to different places; or, as Dr. Lardner suggests, two or more ribbons might be perforated simultaneously, and the message which it contains sent at the same instant to different telegraphic stations, and transmitted in various directions. "In this view of the question," says Dr. Lardner, "the system of Bain is to the common telegraph what the steam-engine is to the horse, the power to the hand-loom, the lace frame to the cushion, the self-acting mule to the distaff,-or the stocking-frame to the knitting needle."

With such peculiar advantages, which we trust will soon be realized, all letters which require despatch will be sent by telegraph, and the post-office will be employed only for sending heavy orders or letters, when there is no occasion for extraordinary celerity of transmission. When the sixpenny or the penny telegraph comes into play, Mr. Bain will stand forth as the greatest of our telegraphic inventors, and Scotland will be able to boast that the telegraph was invented and perfected within her domains. Mr. Bain has hitherto, like all other great inventors, been

unfortunate in not deriving from them those material benefits which their invention so amply confers upon others; but we trust that the time is not distant, when his merits will be appreciated and rewarded.

Mr. Bain's Electro-chemical Telegraph is in use upon 1,200 miles in the United States, and such is its value, as we are informed by Mr. Whitworth, in his Report on the Industrial Exhibition of New York, that in damp and rainy weather, when Morse's telegraph works imperfectly, they find it convenient to remove the wires from it, and connect them with Bain's in which "they find it practicable to operate when communication by Morse's system is interrupted."

A very ingenious and striking modification of the Electro-chemical Telegraph has been invented by Mr. Bakewell, and was rewarded with a Council Medal at the great Exhibition. It has been called the Autographic Telegraph from its conveying the message actually written in the handwriting of the person that sends it. The message is written upon a sheet of tinfoil, with a thick ink like varnish, which, when dry, is a non-conductor of electricity. This sheet is rolled round a metallic cylinder, so that the lines of the writing are parallel to its axis. A blunt steel point or style is made to move over the message in lines, parallel to the axis of the cylinder which revolves round its axis, as if the steel point were obliterating the message by a number of parallel lines. The style, like that in Bain's telegraph, is connected with the telegraphic wire, at the other end of which is a similar steel point, which draws similar lines upon a sheet of paper wetted with a solution of prussiate of potash, and rolled upon a metallic cylinder. When the style, which passes over the written message, rests upon the tinfoil, the electric current passes along the wire, and the writing style at its farther extremity makes a blue line, but whenever it passes over the non-conducting varnish, the current is stopped. and the recording style leaves a white space of the same breadth as the breadth of the varnished lines. In this way, when the style has passed over the whole of the message in parallel lines, the recording style will have left the message written in white letters of exactly the same form, and relieved by the blue ground produced by the blue lines drawn on the chemically prepared paper. This operation is analogous to that of the workman who is cutting letters upon boxwood for a wood-cut. In cutting out the letter O, for example, he cuts away all the wood excepting what forms the circle. In

« VorigeDoorgaan »