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A History of Wireless Telegraphy (2nd edition, revised), J. J. Fahie, 1901, pages 40-47:
E. AND H. HIGHTON--1852-72.
The brothers Edward and Henry Highton, who were well-known inventors in the early years of electric telegraphy, took up the problem of transaqueous communication about 1852. In Edward Highton's excellent little book, 'The Electric Telegraph: Its History and Progress,' published in that year, he says: "The author and his brother have tried many experiments on this subject. Naked wires have been sunk in canals, for the purpose of ascertaining the mathematical law which governs the loss of power when no insulation was used. Communications were made with ease over a distance of about a quarter of a mile. The result, however, has been to prove that telegraphic communications could not be sent to any considerable distance without the employment of an insulated medium."
On the other hand, Henry Highton long continued to believe in its practicability, and made many further experiments to that end. These were embodied in a paper read before the Society of Arts on May 1, 1872 (Telegraphy without Insulation), from which I condense the following account:--
"I have for many years been convinced of the possibility of telegraphing for long distances without insulation, or with wires very imperfectly insulated; but till lately I had not the leisure or opportunity of trying sufficient experiments bearing on the subject. I need hardly say that the idea has been pronounced on all hands to be entirely visionary and impossible, and I have been warned of the folly of incurring any outlay in a matter where every attempt had hitherto failed. But I was so thoroughly convinced of the soundness of my views, and of the certainty of being able to go a considerable distance without any insulation, and any distance with very imperfect insulation, that I commenced, some three or four months since, a systematic series of experiments with a view to test my ideas practically.
"I began by trying various lengths of wire, dropped in the Thames from boats, and found that I could, without the slightest difficulty, exceed the limits allowed hitherto as practicable. This method, however, was attended with much difficulty and inconvenience, owing to the rapidity of the tides and the motion of the boats. I next tried wires across the Thames, but had them broken five or six times by the strength of the current and by barges dragging their anchors across them.
"I then put the instrument in my own room, on the banks of the river, and sent a boat down stream with a reel of wire and a battery to signal to me at different distances. The success was so much beyond my expectations, that I next obtained leave to lay down wires in Wimbledon Lake. As the result of all these experiments I found that water is so perfect an insulator for electricity of low tension that wires charged with it retained the charge with the utmost obstinacy; and, whether from the effect of polarisation (so-called), or, as I am inclined to suppose, from electrisation of the successive strata of water surrounding the wire, a long wire, brought to a state of low electrical tension, will retain that tension for minutes, or even hours. Notwithstanding attempts to discharge the wire every five seconds, I have found that a copper surface of 10 or 12 square feet in fresh water will retain a very appreciable charge for a quarter of an hour; and even when we attempt to discharge it continuously through a resistance of about thirty units [ohms], it will retain an appreciable though gradually decreasing charge for five or six minutes. 28
"Since that time I have constructed an artificial line, consisting of resistance coils, condensers, and plates of copper in liquids, acting at once as faults and as condensers, so that I might learn as far as possible to what extent the principle of non-insulation can be carried, and I have satisfied myself that, though there are difficulties in very long lengths absolutely uninsulated, yet it is quite feasible to telegraph, even across the Atlantic, with an insulation of a single unit instead of the 170,000 units [absolute] of the present cables.
"The instrument with which I propose to work is the gold-leaf instrument, constructed by me for telegraphic purposes twenty-six years ago, 29 acted upon by a powerful electro-magnet, and with its motions optically enlarged. The exclusive use of this instrument in England was purchased by the Electric and International Telegraph Company, but it was never practically used, except in Baden, where a Government commission recommended it as the best. One of its chief merits is its extreme lightness and delicacy. Judging by the resistance it presents to the electric current, it would appear that the piece of gold-leaf in the instrument now before us does not weigh more than 1/2000th part of a grain; let us even say that it weighs four times more, or 1/500th part of a grain. In order, then, to make a visible signal we only have to move a very, very small fraction of a grain through a very, very small fraction of an inch. You may judge of its delicacy when I show you that the warmth of the hand, or even a look, by means of the warmth of the face turned towards a thermopile, can transmit an appreciable signal through a resistance equal to that of the Atlantic cable (experiment performed). Another great merit of this instrument is its ready adaptability to the circumstances in which it may be placed, as it is easy to increase or diminish the length, or breadth, or tension of the gold-leaf. Thus, increase of length or diminution of breadth increases the resistance, but also increases the sensitiveness; and again, partaking as it does partly of the character of a pendulum and partly of a musical string, the rapidity of vibration is increased by giving it greater tension and greater shortness (though by doing so the sensitiveness is diminished), so that you can adjust it to the peculiar circumstances of any circuit. Again, you notice the deadness of the movements and the total absence of swing, which, whenever a needle is used, always more or less tends to confuse the signals. The greatest advantage of all is that we can increase the sensitiveness without increasing the resistance, simply by increasing the power of the electromagnet.
"Having now explained the construction of the instrument, and pointed out its merits, I proceed to show by experiment how tenaciously a piece of copper in water will retain a state of electrical tension. Here is a tub of fresh water, with copper plates presenting to each other about 14 square feet of surface. I charge these plates with a Daniell cell, and you see how they retain the charge; in fact, they will go on gradually discharging for several minutes through the small resistance of the gold-leaf instrument. I now do the same with a tub of salt water, and the result is still the same, though less marked. In fact, these plates, with the water between, represent the two metallic surfaces of a Leyden jar, and the water retains the electricity of this small tension with much more obstinacy than the glass of a Leyden jar does the electricity of a higher tension. 30
"Indeed, it is a fact of the highest importance in telegraphy that when there is a fault, electricity of a high tension, say of twenty or thirty Daniell cells, will almost wholly escape by it, and leave nothing for the instrument; whereas electricity of a small tension, as from a single cell of large surface, will pass through the instrument with very little loss of power. This is strikingly shown by the use of an ordinary tangent galvanometer. I cannot well show it to a large audience like the present, therefore I will only inform you that when I have taken two currents, each marking 30° on the galvanometer, the one of high tension from thirty Daniell cells, and the other of low tension from a single cell of small internal resistance, a fault equivalent to the exposure of a mile of No. 16 wire in sea-water will annihilate all appreciable effects on the galvanometer when using the current of high tension, whereas the current of low tension will still show as much as 20°. You see, then, the importance of using currents of low tension from a battery of large surface, and how a faulty cable can be worked with such currents when it is absolutely useless with currents of high tension.
"There are three ways of signalling without insulation: one, only feasible for short distances; a second, which I think will be found the most practicable; and a third, in the practical working of which for very long distances several difficulties (though by no means insuperable) present themselves.
"To explain the first plan, we will take the case of a river, and in the water near one bank place the copper plates A B, and connect them with a wire, including the battery P. Near the opposite bank submerge similar plates, C D, connected by a wire, in the circuit of which is placed the galvanometer g. Between A and B the current will pass by every possible route, in quantities inversely proportional to their resistances; parts will pass direct by A B; and other portions by A, C, D, B, and by A, C, g, D, B. Now, if the plates be large, and A C and B D respectively comparatively near to each other, an appreciable current will pass from A to C, through g, and back from D to B; but if the plates be small, the battery power small, and the distance from A to B and from C to D comparatively short, no appreciable amount will pass through the galvanometer circuit. I do not hesitate to say that it is possible, by erecting a very thick line wire from the Hebrides to Cornwall, by the use of enormous plates at each extremity, and by an enormous amount of battery power--i.e., as regards quantity--to transmit a current which would be sensibly perceived in a similar line of very thick wire, with very large plates, on the other side of the Atlantic. But the trouble and expense would probably be much greater than that of laying a wire across the ocean.
"The second is the simplest and most feasible plan--namely, laying across the sea two wires kept from metallic contact with each other, and working with that portion of the current which prefers to pass through this metallic circuit instead of passing across the liquid conductor, using currents of low tension from batteries of large surface.
"The third method is to lay a single wire imperfectly insulated, and to place at the opposite end beyond the instrument a very large earth-plate. Any electrical tension thrown on this wire transmits itself more or less to the opposite end, and will be shown on any instrument of small resistance and sufficient delicacy. 31 There are certain difficulties in this way of working, such as the effects of earth-currents and currents of polarisation which keep the needle or gold-leaf permanently deflected from zero, necessitating special means of counteraction. I have no doubt, from my experiments, that these difficulties may be overcome; but still I think the simplest and most feasible, and not more expensive, plan will be to work with two naked wires kept apart from metallic contact, using electricity of a very low tension."
Soon after this Mr Highton turned a complete volte face, and went back to wires perfectly insulated, but at a ridiculously small cost! On April 20, 1873, he sent the following letter to the 'Times':--
"SIR,--Some months ago I read a paper to the Society of Arts on the possibility of telegraphing for great distances without insulation, for which they were good enough to vote me a medal. I now find, however, that by the discovery of a new insulating material perfect insulation can be provided at a ridiculously small cost.
"I find by the addition of this material, which is simply tar chymically modified, nearly 200,000 per cent is added to the insulating power of a thin coating of gutta-percha. I hope the result will shortly be found in the great cheapening of telegraphy.--Yours, &c.,
The new material here referred to was a preparation of vegetable tar and oxide of lead, which almost instantly solidified on application. In some experiments at the Silvertown Works, it was found that No. 18 copper wire, covered with gutta-percha weighing only 21 lb. to the mile, had its insulation increased nearly 200,000 per cent, representing an insulation per mile of nearly three billion ohms!--enough, as the inventor needlessly remarked, for any lengths possible on the surface of the earth. 32
28 It does not appear to have struck our author that these effects would militate against the practical application of the method.
29 A special arrangement of this instrument, adapting it for long and naked (or badly insulated) lines, was patented February 13, 1873. For reports of its great delicacy, see 'Telegraphic Journal,' February 15, 1874.
30 These experiments are not clearly described in the report from which we are quoting. It we understand them aright, they are rather electrolytic than Leyden-jar effects. In any case, as the tubs were presumably fairly well insulated, they have no bearing ad rem.
31 The following cutting from 'Once a-Week' (February 26, 1876) is given here in the hope that some American reader will kindly supply details, if any are procurable: "The 'New York Tribune' gives an account of what appears to be a very remarkable discovery in electrical science and telegraphy. It is claimed that a new kind of electricity has been obtained, differing from the old in several particulars, and notably in not requiring for transmission that the conducting wires shall be insulated."
32 For reports on this cable see 'Telegraphic Journal,' vol. ii. pp. 104, 129. The Hightons received several Society of Arts' medals for the excellence of their telegraphic appliances which were largely used fifty years ago. Indeed a company, The British Electric Telegraph Co., was expressly formed in 1850 to work their instruments, and was afterwards merged in the British and Irish Magnetic Telegraph Co. A few years before his death (December 1874) Henry Highton invented an artificial stone, which I believe is largely used in building and paving.
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