Part 21

Dr. Andrew Wilson, in an interesting paper, in which he maintains that sea-serpent tales are not to be treated with derision, but are worthy of serious consideration, “supported as they are by zoological science, and in the actual details of the case by evidence as trustworthy in many cases as that received in our courts of law,” expresses the opinion that plesiosauri and ichthyosauri have been unnecessarily disinterred to do duty for the sea-serpents. But he offers as an alternative only the ribbon-fish; and though some of these may attain enormous dimensions, yet we have seen that some of the accounts of the supposed sea-serpent, and especially the latest narrative by the captain and crew of the _Pauline_, cannot possibly be explained by any creature so flat and relatively so feeble as the ribbon-fish.

On the whole, it appears to me that a very strong case has been made out for the enaliosaurian, or serpent-turtle, theory of the so-called sea-serpent.

One of the ribbon-fish mentioned by Dr. Wilson, which was captured, and measured more than 60 feet in length, might however fairly take its place among strange sea creatures. I scarcely know whether to add to the number a monstrous animal like a tadpole, or even more perhaps like a gigantic skate, 200 feet in length, said to have been seen in the Malacca Straits by Captain Webster and Surgeon Anderson, of the ship _Nestor_. Perhaps, indeed, this monster, mistaken in the first instance for a shoal, but presently found to be travelling along at the rate of about ten knots an hour, better deserves to be called a strange sea creature even than any of those which have been dealt with in the preceding pages. But the only account I have yet seen of Captain Webster’s statement, and Mr. Anderson’s corroboration, appeared in an American newspaper; and though the story is exceedingly well authenticated if the newspaper account of the matter is true, it would not be at all a new feature in American journalism if not only the story itself, but all the alleged circumstances of its narration, should in the long run prove to be pure invention.

_ON SOME MARVELS IN TELEGRAPHY._

Within the last few years Electric Telegraphy has received some developments which seem wonderful even by comparison with those other wonders which had before been achieved by this method of communication. In reality, all the marvels of electric telegraphy are involved, so to speak, in the great marvel of electricity itself, a phenomenon as yet utterly beyond the interpretation of physicists, though not more so than its fellow marvels, light and heat. We may, indeed, draw a comparison between some of the most wonderful results which have recently been achieved by the study of heat and light and those effected in the application of electricity to telegraphy. It is as startling to those unfamiliar with the characteristics of light, or rather with certain peculiarities resulting from these characteristics, to be told that an astronomer can tell whether there is water in the air of Mars or Venus, or iron vapour in the atmosphere of Aldebaran or Betelgeux, as it is to those unfamiliar with the characteristics of electricity, or with the results obtained in consequence of these characteristics, to be told that a written message can be copied by telegraph, a map or diagram reproduced, or, most wonderful of all, a musical air correctly repeated, or a verbal message made verbally audible. Telegraphic marvels such as these bear to the original marvel of mere telegraphic communication, somewhat the same relation which the marvels of spectroscopic analysis as applied to the celestial orbs bear to that older marvel, the telescopic scrutiny of those bodies. In each case, also, there lies at the back of all these marvels a greater marvel yet—electricity in the one case, light in the other.

I propose in this essay to sketch the principles on which some of the more recent wonders of telegraphic communication depend. I do not intend to describe at any length the actual details or construction of the various instruments employed. Precisely as the principles of spectroscopic analysis can be made clear to the general reader without the examination of the peculiarities of spectroscopic instruments, so can the methods and principles of telegraphic communication be understood without examining instrumental details. In fact, it may be questioned whether general explanations are not in such cases more useful than more detailed ones, seeing that these must of necessity be insufficient for a student who requires to know the subject practically in all its details, while they deter the general reader by technicalities in which he cannot be expected to take any interest. If it be asked, whether I myself, who undertake to explain the principles of certain methods of telegraphic communication, have examined _practically_ the actual instrumental working of these methods, I answer frankly that I have not done so. As some sort of proof, however, that without such practical familiarity with working details the principles of the construction of instruments may be thoroughly understood, I may remind the reader (see p. 96) that the first spectroscopic battery I ever looked through—one in which the dispersive power before obtained in such instruments had been practically doubled—was of my own invention, constructed (with a slight mechanical modification) by Mr. Browning, and applied at once successfully to the study of the sun by Mr. Huggins, in whose observatory I saw through this instrument the solar spectrum extended to a length which, could it all have been seen at once, would have equalled many feet.[27] On the other hand, it is possible to have a considerable practical experience of scientific instruments without sound knowledge of the principles of their construction; insomuch that instances have been known in which men who have effected important discoveries by the use of some scientific instrument, have afterwards obtained their first clear conception of the principles of its construction from a popular description.

It may be well to consider, though briefly, some of the methods of communication which were employed before the electric telegraph was invented. Some of the methods of electric telegraphy have their antitypes, so to speak, in methods of telegraphy used ages before the application of electricity. The earliest employment of telegraphy was probably in signalling the approach of invading armies by beacon fires. The use of this method must have been well known in the time of Jeremiah, since he warns the Benjamites “to set up a sign of fire in Beth-haccerem,” because “evil appeareth out of the north and great destruction.” Later, instead of the simple beacon fire, combinations were used. Thus, by an Act of the Scottish Parliament in 1455, the blazing of one bale indicated the probable approach of the English, two bales that they were coming indeed, and four bales blazing beside each other that they were in great force. The smoke of beacon fires served as signals by day, but not so effectively, except under very favourable atmospheric conditions.

Torches held in the hand, waved, depressed, and so forth, were anciently used in military signalling at night; while in the day-time boards of various figures in different positions indicated either different messages or different letters, as might be pre-arranged.

Hooke communicated to the Royal Society in 1684 a paper describing a method of “communicating one’s mind at great distances.” The letters were represented by various combinations of straight lines, which might be agreed upon previously if secrecy were desired, otherwise the same forms might represent constantly the same letters. With four straight planks any letter of this alphabet could be formed as wanted, and being then run out on a framework (resembling a gallows in Hooke’s picture), could be seen from a distant station. Two curved beams, combined in various ways, served for arbitrary signals.

Chappe, in 1793, devised an improvement on this in what was called the T telegraph. An upright post supported a cross-bar (the top of the T), at each end of which were the short dependent beams, making the figure a complete Roman capital T. The horizontal bar as first used could be worked by ropes within the telegraph-house, so as to be inclined either to right or left. It thus had three positions. Each dependent beam could be worked (also from within the house) so as to turn upwards, horizontally, or downwards (regarding the top bar of the T as horizontal), thus having also three positions. It is easily seen that, since each position of one short beam could be combined with each position of the other, the two together would present three times three arrangements, or nine in all; and as these nine could be given with the cross-bar in any one of its three positions, there were in all twenty-seven possible positions. M. Chappe used an alphabet of only sixteen letters, so that all messages could readily be communicated by this telegraph. For shorter distances, indeed, and in all later uses of Chappe’s telegraph, the short beams could be used in intermediate positions, by which 256 different signals could be formed. Such telegraphs were employed on a line beginning at the Louvre and proceeding by Montmartre to Lisle, by which communications were conveyed from the Committee of Public Welfare to the armies in the Low Countries. Telescopes were used at each station. Barrère stated, in an address to the Convention on August 17, 1794, that the news of the recapture of Lisle had been sent by this line of communication to Paris in one hour after the French troops had entered that city. Thus the message was conveyed at the rate of more than 120 miles per hour.

Various other devices were suggested and employed during the first half of the present century. The semaphores still used in railway signalling illustrate the general form which most of these methods assumed. An upright, with two arms, each capable of assuming six distinct positions (excluding the upright position), would give forty-eight different signals; thus each would give six signals alone, or twelve for the pair, and each of the six signals of one combined with each of the six signals of the other, would give thirty-six signals, making forty-eight in all. This number suffices to express the letters of the alphabet (twenty-five only are needed), the Arabic numerals, and thirteen arbitrary signals.

The progress of improvement in such methods of signalling promised to be rapid, before the invention of the electric telegraph, or rather, before it was shown how the principle of the electric telegraph could be put practically into operation. We have seen that they were capable of transmitting messages with considerable rapidity, more than twice as fast as we could now send a written message by express train. But they were rough and imperfect. They were all, also, exposed to one serious defect. In thick weather they became useless. Sometimes, at the very time when it was most important that messages should be quickly transmitted, fog interrupted the signalling. Sir J. Barrow relates that during the Peninsular War grave anxiety was occasioned for several hours by the interruption of a message from Plymouth, really intended to convey news of a victory. The words transmitted were, “Wellington defeated;” the message of which these words formed the beginning was: “Wellington defeated the French at,” etc. As Barrow remarks, if the message had run, “French defeated at,” etc., the interruption of the message would have been of less consequence.

Although the employment of electricity as a means of communicating at a distance was suggested before the end of the last century, in fact, so far back as 1774, the idea has only been worked out during the last forty-two years. It is curious indeed to note that until the middle of the present century the word “telegraph,” which is now always understood as equivalent to electric telegraph, unless the contrary is expressed, was commonly understood to refer to semaphore signalling,[28] unless the word “electric” were added.

The general principle underlying all systems of telegraphic communication by electricity is very commonly misunderstood. The idea seems to prevail that electricity can be sent out along a wire to any place where some suitable arrangement has been made to receive it. In one sense this is correct. But the fact that the electricity has to make a circuit, returning to the place from which it is transmitted, seems not generally understood. Yet, unless this is understood, the principle, even the possibility, of electric communication is not recognized.

Let us, at the outset, clearly understand the nature of electric communication.

In a variety of ways, a certain property called electricity can be excited in all bodies, but more readily in some than in others. This property presents itself in two forms, which are called positive and negative electricity, words which we may conveniently use, but which must not be regarded as representing any real knowledge of the distinction between these two kinds of electricity. In fact, let it be remembered throughout, that we do not in the least know what electricity is; we only know certain of the phenomena which it produces. Any body which has become charged with electricity, either positive or negative, will part with its charge to bodies in a neutral condition, or charged with the opposite electricity (negative or positive). But the transference is made much more readily to some substances than to others—so slowly, indeed, to some, that in ordinary experiments the transference may be regarded as not taking place at all. Substances of the former kind are called good conductors of electricity; those which receive the transfer of electricity less readily are said to be bad conductors; and those which scarcely receive it at all are called insulating substances. The reader must not confound the quality I am here speaking of with readiness to become charged with electricity. On the contrary, the bodies which most freely receive and transmit electricity are least readily charged with electricity, while insulating substances are readily electrified. Glass is an insulator, but if glass is briskly rubbed with silk it becomes charged (or rather, the part rubbed becomes charged) with positive electricity, formerly called _vitreous_ electricity for this reason; and again, if wax or resin, which are both good insulators, be rubbed with cloth or flannel, the part rubbed becomes charged with negative, formerly called _resinous_, electricity.

Electricity, then, positive or negative, however generated, passes freely along conducting substances, but is stopped by an insulating body, just as light passes through transparent substances, but is stopped by an opaque body. Moreover, electricity may be made to pass to any distance along conducting bodies suitably insulated. Thus, it might seem that we have here the problem of distant communication solved. In fact, the first suggestion of the use of electricity in telegraphy was based on this property. When a charge of electricity has been obtained by the use of an ordinary electrical machine, this charge can be drawn off at a distant point, if a conducting channel properly insulated connects that point with the bodies (of whatever nature) which have been charged with electricity. In 1747, Dr. Watson exhibited electrical effects from the discharges of Leyden jars (vessels suitably constructed to receive and retain electricity) at a distance of two miles from the electrical machine. In 1774, Le Sage proposed that by means of wires the electricity developed by an electrical machine should be transmitted by insulated wires to a point where an electroscope, or instrument for indicating the presence of electricity, should, by its movements, mark the letters of the alphabet, one wire being provided for each letter. In 1798 Béthencourt repeated Watson’s experiment, increasing the distance to twenty-seven miles, the extremities of his line of communication being at Madrid and Aranjuez. (Guillemin, by the way, in his “Applications of the Physical Forces,” passes over Watson’s experiment; in fact, throughout his chapters on the electric telegraph, the steam-engine, and other subjects, he seems desirous of conveying as far as possible the impression that all the great advances of modern science had their origin in Paris and its neighbourhood.)

From Watson’s time until 1823 attempts were made in this country and on the Continent to make the electrical machine serve as the means of telegraphic communication. All the familiar phenomena of the lecture-room have been suggested as signals. The motion of pith balls, the electric spark, the perforation of paper by the spark, the discharge of sparks on a fulminating pane (a glass sheet on which pieces of tinfoil are suitably arranged, so that sparks passing from one to another form various figures or devices), and other phenomena, were proposed and employed experimentally. But practically these methods were not effectual. The familiar phenomenon of the electric spark explains the cause of failure. The spark indicates the passage of electricity across an insulating medium—dry air—when a good conductor approaches within a certain distance of the charged body. The greater the charge of electricity, the greater is the distance over which the electricity will thus make its escape. Insulation, then, for many miles of wire, and still more for a complete system of communication such as we now have, was hopeless, so long as frictional electricity was employed, or considerable electrical intensity required.

We have now to consider how galvanic electricity, discovered in 1790, was rendered available for telegraphic communication. In the first place, let us consider what galvanic or voltaic electricity is.

I have said that electricity can be generated in many ways. It may be said, indeed, that every change in the condition of a substance, whether from mechanical causes, as, for instance, a blow, a series of small blows, friction, and so forth, or from change of temperature, moisture, and the like, or from the action of light, or from chemical processes, results in the development of more or less electricity.

When a plate of metal is placed in a vessel containing some acid (diluted) which acts chemically on the metal, this action generates negative electricity, which passes away as it is generated. But if a plate of a different metal, either not chemically affected by the acid or less affected than the former, be placed in the dilute acid, the two plates being only partially immersed and not in contact, then, when a wire is carried from one plate to the other, the excess of positive electricity in the plate least affected by the acid is conveyed to the other, or, in effect, discharged; the chemical action, however, continues, or rather is markedly increased, fresh electricity is generated, and the excess of positive electricity in the plate least affected is constantly discharged. Thus, along the wire connecting the two metals a current of electricity passes from the metal least affected to the metal most affected; a current of negative electricity passes in a contrary direction in the dilute acid.

I have spoken here of currents passing along the wire and in the acid, and shall have occasion hereafter to speak of the plate of metal least affected as the positive pole, this plate being regarded, in this case, as a source whence a current of positive electricity flows along the wire connection to the other plate, which is called the negative pole. But I must remind the reader that this is only a convenient way of expressing the fact that the wire assumes a certain condition when it connects two such plates, and is capable of producing certain effects. Whether in reality any process is taking place which can be justly compared to the flow of a current one way or the other, or whether a negative current flows along the circuit one way, while the positive current flows the other way, are questions still unanswered. We need not here enter into them, however. In fact, very little is known about these points. Nor need we consider here the various ways in which many pairs of plates such as I have described can be combined in many vessels of dilute acid to strengthen the current. Let it simply be noted that such a combination is called a battery; that when the extreme plates of opposite kinds are connected by a wire, a current of electricity passes along the wire from the extreme plate of that metal which is least affected, forming the positive pole, to the other extreme plate of that metal which is most affected and forms the negative pole. The metals commonly employed are zinc and copper, the former being the one most affected by the action of the dilute acid, usually sulphuric acid. But it must here be mentioned that the chemical process, affecting both metals, but one chiefly, would soon render a battery of the kind described useless; wherefore arrangements are made in various ways for maintaining the efficiency of the dilute acid and of the metallic plates, especially the copper: for the action of the acid on the zinc tends, otherwise, to form on the copper a deposit of zinc. I need not describe the various arrangements for forming what are called constant batteries, as Daniell’s, Grove’s, Bunsen’s, and others. Let it be understood that, instead of a current which would rapidly grow weaker and weaker, these batteries give a steady current for a considerable time. Without this, as will presently be seen, telegraphic communication would be impossible.

We have, then, in a galvanic battery a steady source of electricity. This electricity is of low intensity, incompetent to produce the more striking phenomena of frictional electricity. Let us, however, consider how it would operate at a distance.

The current will pass along any length of conducting substance properly insulated. Suppose, then, an insulated wire passes from the positive pole of a battery at a station A to a station B, and thence back to the negative pole at the station A. Then the current passes along it, and this can be indicated at B by some action such as electricity of low intensity can produce. If now the continuity of the wire be interrupted close by the positive pole at A, the current ceases and the action is no longer produced. The observer at B knows then that the continuity of the wire has been interrupted; he has been, in fact, signalled to that effect.

But, as I have said, the electrical phenomena which can be produced by the current along a wire connecting the positive and negative poles of a galvanic battery are not striking. They do not afford effective signals when the distance traversed is very great and the battery not exceptionally strong. Thus, at first, galvanic electricity was not more successful in practice than frictional electricity.

It was not until the effect of the galvanic current on the magnetic needle had been discovered that electricity became practically available in telegraphy.