Lighthouses of the Future

By Sir William Thomson, LL.D., F.R.S.

Article from Good Words, 1873, pp. 217-224.

[Note: this version is missing the two charts, which can be found in Google Books' scanned version.]

A SHIP sailing from the west, bound for Liverpool, shapes her course for Cape Clear. For four days the weather has been cloudy, and no "sights" of sun or stars have been obtained. From the "dead reckoning," the latitude is estimated at 51° 15′, and the longitude 11° 18′, at four P.M. on the 10th of September, 1873; Cape Clear, 68 miles distant E. by S.½S. The ship is hove to and the deep sea-lead cast, and no bottom is found. Again at seven in the evening the lead is cast—no bottom at 90 fathoms. An hour later the captain, a cautious man, and thorough navigator, heaves to, and casts the lead again. This time he finds bottom at 75 fathoms. Knowing that the Irish coast is well lighted, he stands on his course of E.S.E. at an estimated rate of 8½ knots through the water, and looks out anxiously for the Fastnet. It is flood tide, equinoctial springs, and he has a knot or a knot and a half with him eastward, he believes. Three-quarters of an hour later a light, faintly visible, is made out on the port bow, and almost instantly disappears. After three or four minutes it is seen again, and in the course of the next ten minutes it is seen five or six times each time appearing and disappearing rapidly. This is decidedly the Fastnet, seen just half an hour earlier than was expected from the soundings, and the captain is well pleased. (See chart of Cape Clear, Dingle Bay, 219.) Heavy showers come on, and the light is only seen two or three times again until about ten o'clock, when in intervals between the showers it is seen several times on the port beam, shining out, and becoming eclipsed rapidly, as is the way with a revolving light. The captain alters his course by a point and a half to E. half S., and expects to see the Old Head of Kinsale light half an hour after midnight. At a quarter past ten his ship is ashore on the south end of Vickillane Island, on the north side of the entrance to Dingle Bay. The dead reckoning had given about 40 miles south and 24 miles east of the true position at four in the afternoon, a by no means large error on a five days' run without sights. A careful navigator would, of course, be quite prepared for such an error in the dead reckoning; but in this case the captain, after having felt his way cautiously by soundings, was thrown off his guard by making out a revolving light just in the position in which he expected to see the Fastnet. If he had seen a flashing light or a fixed light, he would have known it was the Calf or the Skelligs, and altered his course accordingly; but having made out a revolving light, he did exactly as almost every man would have done in such circumstances. On behalf of the existing system, it may be urged that the Tearaght light which he had taken for the Fastnet revolves in a minute and a half, whereas the Fastnet revolves in two minutes. This defence is utterly invalid. It is scarcely possible for any one, counting time to himself on a gusty, showery night at sea, to distinguish a one-and-a-half minute from a two-minute revolving light. It is never convenient, and it is often impossible, to find the period of a light by noting on a chronometer the times of its appearances and disappearances.

Take another case. A coaster from the Clyde, bound south, takes refuge from a southerly gale in Belfast Lough. After he has been three days at rest in the snug anchorage of Whitehouse Roads, the wind moderates, and draws more from the west-ward about nightfall. Not wishing to lose more time, he gets under weigh to go to sea the same night, half an hour before high water. He reads in the sailing directions, "The Copeland light in line with Grey Point E.S.E. ¼ E., clears the foul ground on this shore" (the south shore of the Lough, west of Grey Point). His position (A) in the anchorage was such, that Grey Point shut out the Copeland light from his view; so as soon as his anchor is up, he sails N.E. till he sees what he believes to be the Copeland light, well open to the north of Grey Point. (See chart of Belfast Lough, p. 221.) His cargo is of pig iron, and he does not trust his compass, so he does not notice, and, in fact he could not discover that the light bore E. by S.½S. instead of E.S.E. ¼ E., when it first became visible open of Grey Point. He steers for the light, knowing that the ebb tide to the northward will keep him clear of the dangers of the Copeland channel, and he is soon ashore a mile and a half west of Grey Point, at the top of high water. He had really never seen the Copeland light, but had taken for it the clear fixed light of an ironclad, (S) anchored in six fathoms water two miles east of Grey Point.

Passing from imaginary cases, take the real one of the steamer "Cambria," lost on Inistrahul on the 19th of October, 1870. Passengers and crew to the number of 183 perished. One man only, John McGartland, escaped to tell the sad tale. Two days after the event, the keeper of the lighthouse on Inistrahul reports that he and his wife

"on Wednesday, about midnight, heard what appeared to be cries of distress. They opened the lighthouse door, and every gust of wind brought with it shrieks as if from men and women in despair. They also observed a light in the direction of the Tor rocks outside of Inistrahul. This light flickered for a very few minutes, and then disappeared, and soon all was silent. It was a wild, stormy night, and to have ventured out would have been certain destruction."

On the testimony of the lighthouse keeper as to the direction in which the light was seen, it has been inferred that the Cambria foundered not on Inistrahul, but on the Tor rocks.

"The fishermen in the locality say that on Wednesday night there was a strong five-knot tide running east, and the gale also blew from the west."

McGartland stated that some time before the ship struck, two lights had been seen, and the most probable inference is that the lighthouse on Tory Island, showing a fixed white light, visible at a distance of sixteen miles, had been duly sighted, and that afterwards the two-minutes revolving light of Inistrahul had been seen, and lost sight of through the bad weather. If the Inistrahul light had been seen at all, it is certain that it must have been lost sight of; but it is quite possible that it may not have been seen at all. In either case, the invisibility of the light during one minute fifty seconds, out of every two minutes, is largely culpable for the disaster. No one without actual experience in unfavourable weather at sea can fully appreciate how vastly more difficult it is to descry a light which is only visible for a few seconds at a time with long intervals of obscuration, than a fixed light, or a light which is never eclipsed for more than a few seconds at a time.

It is most probable that the light on Inistrahul was not seen on board the "Cambria" till it was too late to alter the course and clear the rocks. The long interval of obscuration—one minute fifty seconds—was quite enough to allow a vessel, running as the Cambria was, under steam and probably canvas, before a gale of wind, to pass unwarned, from a position of safety, to one from which escape was impossible.

Take again the stranding of the "Great Britain," in September, 1846, in Dundrum Bay, on the coast of Ireland, an accident which, though happily without loss of life, caused great damage to that magnificent ship. The "Annual Register," under September 22nd, 1846, says:—

"The ship left Liverpool about eleven o' clock Tuesday morning; and, after clearing the Bell Buoy, bore away under considerable canvas direct in a course for the Calf of Man and the the disaster; and at from four to five o'clock in the afternoon the island was distinctly visible on the starboard bow. Shortly after, it set in to rain and the wind increased; the ship making excellent progress and the passengers uncommonly delighted with the vessel and her admirable qualities as a sea-boat. Night then closed in, dark and wet, and the wind gradually freshened into a half-gale. The log was repeatedly taken. About half-past nine o'clock the passengers were startled by a cry and active movements upon deck, and a general fear prevailed that the ship was in collision with some other vessel. The ship, however, had stranded. The night was dark and stormy, and the ship beat incessantly upon the sand; and the breakers repeatedly breaking heavily over her, one of the lifeboats was carried from its fastenings, on the quarter. The anxious hours of darkness being passed, preparations were made to land the passengers and their luggage; and then it was discovered that the ship had struck upon the soft sandy beach of Dundrum Bay, near the watch-house of Tyrella, a little to the west of the Cow and Calf rocks. Providentially the vessel cleared these dangerous spots; for had it been otherwise, it is more than probable that few, if any, would have escaped. The landing of the passengers was accomplished between the hours of five and seven o'clock on Wednesday morning, and from the protected position of the ship and the nature of the beach, with perfect safety."

The immediate cause of this very serious accident was the mistaking of the single light on St. John's Point, off Dundrum Bay, revolving once in a minute, for the double light on the Calf of Man, revolving every two minutes. Rain and dense haze had prevented the Calf Light off the south end of the Isle of Man from being seen, on the right-hand side, in passing, and the ship, with want of sufficient prudence, had been kept on her course. When later, through the haze, a single revolving light was seen; if this had been known to be the St. John's Light, the ship's course would have been altered to the right, and she would have gone clear in a N.W. direction, along the Irish coast: but the St. John's Light was not marked on the chart used on board the ship, and the light that was seen was taken for one of the two revolving lights on the Calf of Man. So the course was steered to keep clear of the Hen and Chickens rocks, lying to the south-west of the supposed light. One good light on the Calf, if distinguishable from every other light as soon as descried, would, even without knowledge of the comparatively new St. John's Light, have rendered it instantly certain that what was seen really must be, if a shore light at all, a light on the Irish coast, and that the ship's course must be altered to the right.

The Admiralty charts (from which our two charts are copied) mark the different lighthouses, according to one or other of six different descriptions:—F., Fl., F. and Fl., Rev., Int., Alt., in accordance with the following table of abbreviations and explanations, prefixed to the Admiralty list of lights on the different coasts of the world:—

F. Fixed or steady.

Fl. Flashing, showing five or more flashes and eclipses alternately in a minute.

F. and Fl. Fixed light with a white or red flash in addition (preceded and followed by a short eclipse) at intervals of two, three, or four minutes.

Rev. Revolving. Light gradually increasing to full effect, and gradually decreasing to eclipse, at equal intervals of one, two, or three minutes, but occasionally as often as three times in a minute.

Int. Intermittent. Suddenly appearing in view, remaining visible for a certain time, and then as suddenly eclipsed for a shorter time.

Alt. Red and white light alternately at equal intervals, without any intervening eclipse.

A large majority of the lights on the coast of the British Islands are fixed, a considerable number are revolving; and out of 514, in the list corrected to January, 1871, only 29 belong to any of the other descriptions, Fl., F. and Fl., Int., or Alt. A majority of the revolving lights have a period of one minute; very few less than one minute; some as long as three minutes.

Sailors in general look upon lighthouses as works of nature rather than of art, and would as soon think of asking to have the shape of Knockdolian changed, so that it could never be mistaken for Ailsa Craig, as to have the Copeland light altered so as to be not mistakable for a ship's riding light, or for the fixed light of Larne Lough; or to have the periods of revolving and intermittent lights reduced from minutes to seconds; or to have red lights done away with from lighthouses and light-ships, so that it may no longer be possible to mistake them for sailing ships' red side lights. But the faults of our present system of lighthouses are felt by thousands nightly at sea, and borne by them as uncomplainingly as "winter and rough weather."

To every non-official mind it is clear that lighthouses would be much more useful aids to navigation than they are, if each could, as soon as it is descried, be distinguished from any other lighthouse, from any ships' light, and from any ordinary shore light. Why is it then that a simple method for securing this great object, given by the late Charles Babbage twenty-two years ago, is not yet brought into use, and his "Note respecting Lighthouses (Occulting Lights)," remains to this day in the limbo of Trinity House pigeon-holes, Parliamentary Blue Books, and the archives of the Admiralties of maritime nations? In his "Passages from the Life of a Philosopher," (Longman, 1864), the following sentence occurs:—

"It may happen, as is now happening to my system of distinguishing lighthouses from each other, and of night telegraphic communication between ships at sea—that although officially communicated to all the great maritime governments, and even publicly exhibited for months during the Exhibition of 1851, it will be allowed to go to sleep for years, until some official person, casually hearing of it, or perhaps reinventing it, shall have interest with the higher powers to get it quietly adopted as his own invention."

One part of Babbage's invention, the night telegraphic communication between ships at sea, has been adopted with marked success, in the system of signalling by flash lights, introduced practically about ten years ago by Captain Colomb, and now in regular use in our navy, and in submarine cable expeditions. It was found exceedingly valuable in the operations of the Atlantic Telegraph expedition of 1866, by which the cable laid and lost in 1865 was recovered and completed. It seems indeed that the method of signalling by flash lights had been taken advantage of by the Russians very shortly after the time of its publication by Babbage. The following statement is extracted from a letter which appeared in the Times of the 16th July, 1855:—

"To the Editor of the Times.

SIR,—The failure of the Sebastopol assault on the 18th of June has been ascribed to the mistake of a signal made by the general commanding one of the attacks—the fuse of a shell was mistaken for a rocket, the signal previously agreed upon. One of the most extraordinary features of the present war is the singular neglect by the allies of those aids which a highly advanced state of mechanical science places at their disposal.

The Russians, on the contrary, have for years examined and systematically treasured up every invention which could contribute to their success.

It requires no profound military skill to perceive that, under the peculiar features of the localities around Sebastopol, where combined attacks are directed by two commanders-in-chief, it is important that they should possess, if possible, means of instant communication with each other. It is still more important that each commander should have instant means of conveying orders to the leaders of each of his several attacks. Had this been the case, the mistake of a signal would have produced but little inconvenience, because it might, as soon as perceived, have been rectified. The commanders-in-chief might communicate with each other by a portable electric telegraph; but this instrument could not be used by the advancing troops. A more effective instrument would be some simple telegraph, fixed at the two stations chosen by commanders-in-chief.

During a night attack a very simple form of telegraph might be used, which has already been proposed for enabling ships to communicate with lighthouses or other vessels; it is called the 'occulting telegraph.' Its principle is equally valuable for enabling the seamen to read the number of any given lighthouse as soon as it appears above the horizon, or for communicating his own necessity for assistance or the news he brings.

The best lighthouses consist of one argand lamp, surrounded by glasses, which concentrate the greater part of the light in a direction parallel to the surface of the sea. Now, it is well known that if an opaque cylinder is lowered over the glass of an argand burner the light will be entirely hidden. If the shade be lowered, and then quickly raised, the light will suffer a temporary extinction, which is called an 'occulatation.' At whatever distance the lamp can be seen, this occultation will be perceived. It has been found by experiment that if these occultations succeed each other at about the distance of one second, they can not only be seen, but easily counted. Here, then, is a ready means of expressing small numbers. To express large numbers, as, for example, 374, it is only necessary to make three successive occultations, and allow a pause of five seconds; make seven successive occultations, and allow a pause of five seconds; make four successive occultations, and allow a pause of twelve seconds. After this the series may be repeated.

Thus the number 374 can be communicated to all within sight of the lamp in little more than half a minute. One great advantage of this system of signals is, that the number can be repeated by mechanism until it is acknowledged to have been observed.

In the case of a lighthouse, the same number must be repeated from sunset to sunrise. Another advantage is, that this kind of telegraph is adapted to all existing numerical codes of signals. During the day the light of the sun itself might be used for an occulting telegraph. The distance at which sunlight could be employed might, under favourable circumstances, extend to about 100 miles.

In 1851 an occulting was publicly exhibited in London. The plan was at that time communicated to the Trinity House.

Occulting lights were subsequently approved by the Lighthouse Board of the United States, and Congress appropriated 5000 dollars to make experiments upon them.

I have also evidence that the occulting system of lights was known at St. Petersburg in 1853, and I infer that it has been practically applied at Sebastopol from the following extract from a letter of your correspondent at Balaklava (Times, July 11th):—

'A long train of provisions came into Sebastopol to-day, and the mirror telegraph, which works by flashes from a mound over the Belbeck, was exceedingly busy all the forenoon.'

This can scarcely apply to any other than an occulting telegraph.

I am, sir,
Your obedient servant,


Dorset Street, Manchester Square, July 13."

The plan described in the preceding letter for signaling numbers by flashing lights is not the best in detail. Captain Colomb made a great improvement by adopting, instead of it, the ordinary Morse telegraph alphabet, which consists of short signals and longer signals following one another with proper longer and shorter intervals to form groups to designate numbers, letters, or words. In the Morse system of electric telegraph a long ribbon of paper, kept running at a uniform rate by wheelwork, is used to receive longer or shorter marks, exhibiting to the eye a permanent record of the durations of the signals, and of the intervals between them. Originally the marks were made by a stile pressed against the paper, so as to emboss it; now they are universally made by an ink-marker, of which many different forms have been devised and used. The short signal draws a very short line, the long signal a longer line. The alphabet printed on a telegraph ribbon is as follows:—

The short line was called a dot, and the longer line a dash; and now by universal usage the short signal of the Morse alphabet is called a dot, and the long signal a dash, whether they are recorded on paper or not, and whether they are conveyed by electricity, or by sound, or by light, or by any other physical agency. In Colomb's nautical night telegraph short flashes constitute the dots, and longer flashes, the dashes. The exceeding simplicity, ease, and certainty of this system of telegraphing may be easily tested by any reader with no other apparatus than a candle or lamp, and a screen held in the hand. With a Morse alphabet on paper before him, he can in a first trial make signals at a slow speed with perfect accuracy, expressing any letters, words, or sentences he pleases, which can be read as far as the light can be seen by any one knowing the Morse alphabet. Young persons after two or three trials learn both to make and to read with great ease and quickness signals of this kind, and can thus speak to one another easily at night between two houses a mile or two apart. Flash signal lamps are now regularly made for ships at sea, and are already in very general use. A screen lifted up and let down by hand suffices to make the signals: and I believe the signalmen prefer making them thus to using a mechanism which is sometimes attached to the lamp.

The annexed diagram exhibits the system and the proportions of the intervals of light and darkness by which the different letters of the alphabet, each repeated indefinitely, are shown by an "occulting light." The application to lighthouses is exceedingly simple. Each lighthouse must in general, as Babbage says, keep repeating its number (or letter, as I should prefer) from sunset till sunrise. It is easy to produce mechanism by which this will be done automatically with the greatest certainty. In the first place, we have to choose the mode of making the occultations. This may be by a cylindrical screen enclosing the glass shade of the argand burner, and lifted up and let down to let the light be seen, and to eclipse it, as proposed by Babbage. Or it may be by a cylindrical or hollow spherical screen with vertical slits cut in it, of different breadths for the dots and dashes, and with proper spaces of screen between them to produce the eclipses of the required duration. Either method may be adopted to give the eclipses and reappearances of the light with any degree of suddenness required; but the mechanism necessary for the first is much less simple and needs considerably greater driving power than the mere uniform revolution of the second method, which is exactly the same movement as that of the ordinary revolving lights at present in use. The second method has another great advantage, in admitting of the introduction of optical appliances to avoid the total loss of the eclipsed light which is inevitable when the first method is used. It seems, indeed, that in all respects the second method is preferable to the first. But another method, already partially tried with marked success in Ireland in consequence of a suggestion of Dr. Tyndall's, is much preferable in every respect to either of those in all cases in which gas can be used as a substitute for oil in lighthouses. It is simply to almost extinguish the gas instead of eclipsing it during the intervals of darkness between the dots and dashes. I have been much struck with seeing a regularly intermittent lamp in a crowded street in London, and remarking how certainly and how quickly I could distinguish it from hundreds of others, some of them fixed street lamps, and house and shop lights; others carriage and cab lights, flitting about and eclipsing one another incessantly. From the far end of the street there was no difficulty whatever in distinguishing it from all the other lights, even although it was continually being eclipsed irregularly, for a few seconds at a time, by intervening carriages. Its own regular intermittence was of course due to a little water which had lodged in its supply gas pipe; and this suggested to me a frictionless water stopcock, which may be readily worked by a very light and simple mechanism, to give the desired dot and dash signals. A second channel or "bye pass" is to be added to prevent the gas from being completely extinguished during the intervals of obscuration, when the water stopcock is shut. Thus, without any waste whatever of the illuminating material, and with no complication of optical contrivance beyond that of the ordinary fixed Lighthouse, the desired system of signalling Lighthouses may be realised, wherever gas is used as the illuminating material.

The Lighthouse of the future is to be illuminated by gas, except when the situation is an isolated rock at sea, or where for any reason the price of coal is prohibitory. This I judge from a series of able reports by Dr. Tyndall, contained in "Further papers relative to a proposal to substitute gas for oil as an illuminating power in Lighthouses. Presented to both Houses of Parliament by command of Her Majesty. 1871."[1]

A paper (Nov. 8th, 1869,) by John R. Wigham, Gas Engineer, London and Dublin, included in this collection, contains the following statement:—

"The value of using gas in Lighthouses has been fully recognised by the Board of Irish Lights, after a trial of more than four years, and the whole system has been most carefully investigated by Dr. Tyndall, who is, perhaps, the greatest living authority on such subjects, and as his opinion confirms the experience of the Board of Irish Lights, I feel that, supported by such authorities, I may safely leave the decision to the judgment of the Board of Trade."

One of Dr. Tyndall's reports (Oct. 8th, 1870,) contains the following:—

"Now the point to be noted here is, that were gas employed instead of oil, the periods of occultation produced by the screen might, by a simple mechanical contrivance, be produced by the extinction of the gas. In the dark interval no gas would be expended; hence it is certain that the Rockabill Lighthouse[2] might be effectually lighted by half the amount of gas necessary in the case of a fixed light.

But it has been already demonstrated that by the substitution of gas for oil at Howth Baily[3], a saving is effected in the case of that fixed light. Much more, then, would there be a saving at Rockabill, which is as easily accessible as Howth Baily. From the data before me I should infer that the diminution of expense consequent on the change indicated would amount annually to £6o. In this estimate I include the interest on the sum expended in the construction of gasworks."

Again Dr. Tyndall writes on the 7th Feb.,1871:—

"The flexibility, if I may use the term, with which gas lends itself to lighthouse purposes was still further demonstrated, and what appears to be an important modification of an intermittent light hit upon. In a letter addressed to me, on the 27th of January, Mr. Wigham writes thus:—
'While carefully looking into this part of the subject, it occurred to me that we might avail ourselves of this peculiarity of gaslight, to enable us to receive, while the lens was passing the eye,[4] three or four bright flashes instead of only one. I tried it, and found that we had hit upon one of the most striking and distinguishing lights. I asked Captain Hawes to meet me last night, when he told me that he had been thinking of something of the same kind. We then jointly looked at the light, and Captain Hawes is perfectly charmed with the effect. The impression that you receive when you first look at it is that there is life in it, and that it is actively exerting itself to warn the mariner of some danger. The observations of this new form of intermittent light have been assiduously continued.'

The result is described in the following letter, which has been addressed to me by Captain Hawes:—

'Office of Irish Lights, Dublin, 1st Feb., 1870.

Dear Sir,—Since writing to you last I have gone a good deal more into the matter of the use of gas for annular lenses, and have requested Mr. Wigham to make many experiments on the subject. We had just succeeded in reducing the small secondary flash[5] to which your last note alluded, to an exceeding trifling twinkling light, when we devised an improvement upon the method of saving gas, which we showed to you when you were here, and have succeeded in producing an exceedingly beautiful and distinguishing light; it consists in causing the gas to produce, while each lens passes the eye, three or four rapid flashes caused by the extinction and re-ignition of the gas. We first had this light fixed on the roof of Messrs. Edmundson's factory, and I observed it from the upper windows of this house, and confess I was very much delighted with its performance, and I think I never saw any light that seemed to me more suitable for catching the eye of the mariner. Wishing to ascertain whether the same appearance would be seen by a person at a greater distance, I had the lens removed to the experimental house at Howth Baily, and for the last two evenings have been witnessing the effect at Kingstown.

My previous favourable impressions are more than confirmed by these observations. There are, as you know, a great many lights about Kingstown harbour, &c., but whenever the flashes of this new light were displayed, they caught the eye as a flash of a gun would, even although not exactly turned in the direction of the lighthouse.

I look upon this matter as one of exceeding importance, and would be glad to hear from you on the subject. You will observe from the foregoing that, while the saving of the gas by its extinction is not accomplished exactly in the same mode as you described in your last report to the Board of Trade, yet that the main gist of your report, viz., the saving of the gas, is effected to the same extent as you stated . . . . . I should very much like to see gas introduced for Rockabill lighthouse, and am persuaded by this new system of rapid flashes, many most desirable things, for example connected with signalling, which we now hardly think of, might be accomplished.

I am, &c.,
     E. H. Hawes, Inspector of Lights.'

Dr. John Tyndall, F.R.S., &c.,
     Royal Institution of Great Britain."

Dr. Tyndall concludes his report, from which the foregoing passages are extracted with the following important statement:—

"The Board may, I think, feel confident that, before finally recommending any change in our system of lighthouse illumination, I shall assure myself by suitable experiments that the change would be an improvement optically or economically. That gas is capable of manifold application in lighthouses is even now evident. We have to deal in fact with two elements, the quantity of the light and its distribution. On the former score, gas in Ireland competes successfully with oil; but it is to the ease and promptness with which gas lends itself to various modes of distribution that the chief manifestations of its superiority are to be looked for. I anticipate great ameliorations and advances from its future use."

The only practical objection I have ever heard made to the universal adoption of the automatic signalling system for lighthouses ignores the use of gas, with the perfectly economical obscurations which it allows; and is that the "occultations" involve a loss of light. I answer unqualifiedly that they will never involve a loss of useful light. Of all the best lighthouses on the present system, the fixed lights are practically the most sure to be descried in unfavourable circumstances. One of these lights, converted into a self-signalling light by simply an opaque unsilvered screen, either on Babbage's plan, or revolving as I have proposed, would certainly be not less easily seen at a distance than it is at present, provided the eclipse be never longer than two seconds, and the time of full brightness never less than half a second. It is probable, indeed, that the rapid contrasts presented to the eye would render the intermittent light more easily descried than a fixed light of equal intensity. But whether more easily descried, or only as easily descried, it is certain that the noneclipsed part of the light would do much better service to navigation than the whole light does as a "fixed light" of our present system. Let Hesiod then answer those who object to the conversion of fixed lights into self-signalling lights:—Νήπιοι οὐδ᾽ ἴσασιν ὅσῳ πλέον ἥμισυ παντός—foolish persons, they don't know how much better is half than the whole.

Why, I repeat, have not automatic signalling lights been already adopted by all the lighthouse boards of the world? Many truthful replies may no doubt be given to this question; but there is only one answer: the authorities were not sufficiently impressed with the importance of the object proposed. Had they been so, they would never have accepted the reports of their engineers and other scientific advisers, condemning Babbage's proposal. If they were told the thing could not be done, they would have sent back orders to their engineers to do it. If they were told it would involve waste of oil, they would have directed their engineers and opticians to find how to do it without wasting oil. But they were told it was not of much use, or were not sufficiently told that it is of enormous importance; and the proposal was shelved. I have absolute confidence in asserting that, if the British Parliament resolves that the object is of importance, and votes a moderate sum for putting Babbage's suggestion into practice, in three or four lighthouses representing different classes of its application, at first without waiting for economy of gas or oil, the most obstructive of anti-reformers and the most apathetic of boards will be thoroughly converted; and before many years we shall have an economy of oil and gas, of property at sea, and of life, superior to any hitherto attained in our lighthouse system.


Related Quotes & References:

"Different Forms of Light for Lighthouses.—At the recent meeting of the British Association Sir W. Thomson and Mr. J. Hopkinson read a paper on 'Methods for giving Distinctive Characters to Lighthouses.' Sir William Thomsons read the first portion. Speaking of coloured lights, he said they would not be of value except for marking a specific direction, and for this colour had been the only successful invention. At Ardrossan a ship went ashore through a mistake of a light in Ardrossan for a harbour light. There was a red light in an apothecary's shop in Ardrossan, and the pilots had told him that they regularly steered in by the 'light of the doctor's shop.' The greater speed of steam traffic required that light should be seen at a greater distance and recognised sooner, and the lights must be more powerful. Rapid advances have been made in the English lights, particularly in respect to their power, but more distinctions were required. Many harbour lights were now confounded with gas. Now there was a blaze of gas, and it was, in some cases, impossible to make out which was which. The authorities were exceedingly sluggish in making such changes as were required in the appliances. The eclipse light, which he advocated, would signal three lights, which he described as 'short, short, long,' indicating the periods for which the light would be eclipsed. Mr. Hopkinson had also invented a revolving light, which cost little more than the ordinary revolving apparatus, but which would give a double flash or a treble flash, instead of the one flash of the ordinary revolving apparatus." [The Popular Science Review, Vol. xiv, 1875, p. 431.]

"Instead of using common words, the names are spelled out in high and low tones, or by long and short sounds, or by dots and dashes, but generally by long and short sounds, which are to the telegraphist as clear and distinct as language. ... By this code a lighthouse might be flashing out its name all night long in this telegraphic language. And not only could it do so by means of light, but it could do so by means of sound. They only need arrange the fog-horns, Sirens, or whistles, to repeat these signals after each other in a certain preconcerted way, so that, whether by day or night, in clear weather or fog, a mariner who has once learned this language, when he came within range of a lighthouse could not fail to know where he was." [Quoted in "Life of Sir James Nicholas Douglass" by Thomas Williams, 1900]

"Lord Kelvin was the author of the plan of furnishing lighthouses with eclipsing lights in order that they could be easily distinguished. The dark intervals in the light were of two kinds, long and short, corresponding to the dots and dashes of the Morse code. A lighthouse might thus flash out the initial letters of its name. Now if Lord Kelvin had bluntly laid before the Admiralty his suggestion that lighthouses should advertise themselves in this way, the suggestion would probably have been recognised as an 'ingenious' idea and as such it would have been opposed and scouted. He, therefore, in the first instance merely suggested that lighthouse lights should have long and short eclipses. Lights so arranged, he said, could easily be distinguished from the masthead light of a steamer. The authorities consulted used their own reasoning. They realised that they, as practical men, could easily distinguish a light that has a series of long and short eclipses from a light that had none. After the suggestion had been adopted Lord Kelvin allowed it to be known that the eclipses made dots and dashes on the Morse system. In a letter written in 1875 he says: 'But I keep in the background the fact that, adhering simply to the letters of the Morse alphabet, we can with the greatest ease give twenty-eight distinctions, each thoroughly unmistakable for any other. This has a tendency to frighten "practical" men.'" ["Common Sense and Its Cultivation" by Hanbury Hankin, 1999, p. 197]

Also see Kelvin's "On Lighthouse Characteristics", Popular Lectures and Addresses, Vol. iii, p. 389.