How to signal 100 miles without the aid of electricity. What is a heliograph?

The Journal of the Royal United Services Institute (Great Britain) for Defence Studies Volume 19 in 1875 recounts a meeting that discusses the heliograph and its inventor. The discussion and history are fascinating. There is even some dissent expressed at the heliographs ultimate value. But since the copyright has expired, I’ll take the liberty of quoting the entire article:

The duty I have undertaken this evening of offering a brief explanation of the construction and use of the Heliograph would have devolved more appropriately upon its inventor Mr Henry C. Mance, of the Government Persian Gulf Telegraph Department, but as he is on service in India and is consequently prevented from appearing before you I have been induced to attempt it for him. Beyond the fact that the invention has been placed by Mr Mance in my charge and that I have had some practical acquaintance with its working capabilities there is nothing to justify me in addressing an assembly like the present on a subject in which so many purely military questions are involved. I have however been put in possession of the results of the numerous experiments made by Mr Mance and have had the further advantage of reading the reports of the several skilled officers to whom the instrument has been entrusted for trial by the Government of India. It is upon the facts embodied in these reports that the suggestions I may venture to offer as to the adaptability of the instrument to military uses are chiefly based and if I travel into further inferences I beg you to regard them as submitted to the consideration of those of my hearers who may do me the honor to refer them to the test of their own knowledge and experience. My chief encouragement lies in the hope that the merits of the instrument will in some measure make up for all defects in its description. I should have no doubt on that point if this meeting had been assembled on a clear sunny afternoon on Dover cliffs to conduct a conversation through its instrumentality with another party similarly equipped at Calais. To those who have not studied the phenomena attending the reflection of sunlight first experiments with the heliograph could not fail to be interesting. The most astonishing of them is the immense distance at which the flash can be seen bright and distinct as a planet which in appearance it very much resembles. Many of my hearers will scarcely be prepared to credit that signals from the smaller of the instruments before them which has a mirror of 4 inches diameter are clearly visible under favourable atmospheric conditions without the aid of a telescope at 25 and 30 miles; while from mirrors of 8 and 12 inches they are equally clear at 50, 80, and even 100 miles. The fact is so startling when brought home to one by experiment and in combination with an apparatus by which the flashes can be truly directed and so made to appear and disappear as to represent words that the judgment is liable to fall captive to the imagination in forming an estimate its practical value. For here is an instrument giving any person intelligence the power after a few hours instruction of transmitting messages at a rapid rate in any direction and to any distance which is in fact a complete telegraph without batteries or wires as portable as a rifle and only about half its weight. Experience soon shows however that on ordinary occasions its utility is greatly circumscribed by the necessity of two conditions which do not always exist especially in a climate like that of England viz the presence of sunshine and the absence of obstacles between the points of communication. But before entering on the advantages or disadvantages attending its use, I will ask your attention to the construction of the instrument. The heliograph consists of a mirror mounted on a suitable stand with adjustments to revolve and incline it so that the sun’s rays can be reflected with ease and precision in any required direction. The horizontal movement is obtained by a tangent screw in contact with a wheel on the axle of which is also a revolving plate carrying the mirror the vertical inclination is altered by screwing a steel rod through a nut attached to the top of the mirror. Both adjustments are so constructed as to admit of the reflection being thrown at once approximately true then absolutely so and so kept notwithstanding the ever changing position of the sun. By pressing the tangent screw outwards it is removed from contact with the wheel the plate is then revolved freely by the hand to the required place. The rod attached to the top of the mirror slides into a cylindrical handle at the back until the desired elevation is attained it is then clamped and by a slight movement of the tangent screw or the rod the lateral or vertical inclination of the mirror can be adjusted to the utmost nicety. The cylindrical handle is connected by a ball socket joint with a lever attached to the revolving plate so that the lever handle and rod together form a finger key The depression of this key slightly alters the inclination of the mirror which is restored on the pressure being removed by a spring beneath the lever. Thus by the action of the finger key the reflection of the mirror can be thrown on and off any given spot and by varying the duration of the pressure the flashes are made long or short. By combining these long and short flashes which are equivalent to the dashes and dots of the Morse Code the letters of the alphabet are indicated and the transmission of verbal messages is made possible. Good signallers can send them at the rate of twelve or fifteen words per minute. A very simple means is adopted to ensure the flash being directed truly. It will be observed that a small portion of quicksilver is removed from the centre of the mirror giving it the appearance of having a hole in it. Through this the signaller looks toward the station with which he wishes to communicate while a sighting rod is set up about ten yards before him in a true line with it. A metal stud answering to the sight of a rifle is then slid upwards or downwards on the rod until the centre of the mirror the stud and the distant station are truly aligned. This done however much the mirror is revolved the alignment is never disturbed inasmuch as the centre being the axis on which it moves is stationary. It follows as a matter of course that when the flash from the mirror is thrown on the stud it is in a right line with and is visible from the station beyond at which it is directed. The signaller has therefore only to take care that the flash rises to the stud every time the finger key is depressed. The observer has merely to look towards the signalling station when a succession of bright starlike appearances meets his gaze which he can readily interpret into words. On the sighting rod slides also a short cross bar. It is placed at the same distance beneath the stud as the pressure of the finger key rises the flash on the rod and so that when the mirror is at rest the flash falls on the bar its centre coinciding with the point of intersection. As the position of the sun alters the flash would gradually move from this central position to which it must be preserved by a slight turn at intervals of the tangent screw and vertical adjustment. The rod thus serves as an object on which to throw the flash and thus of ascertaining its whereabouts it also affords a means of directing the flash truly. Both rod and bar are usually made of white wood the reflection being more visible on a white than on a dark substance. It is evident that if it were required to send the flash in a direction precisely opposite to the sun a difficulty would arise but it is easily obviated by employing a second instrument its function being to reflect the rays back into the first which then flashes them to the required spot with as much ease as if no intermediary had been employed. A second apparent difficulty that of making a true alignment with a station twenty or fifty miles off has in reality no existence. It is easy to attract the attention of a look out however distant; he responds with a rightly directed flash from his instrument and at that starlike appearance the original signaller aims with as much ease as he would at the moon. It may be added that as the vertical adjustment forms part of the finger key the movement necessary to obviate the changing position of the sun can be made while in the act of signalling one hand being also at liberty to control the tangent screw. The next subjects on which I think you will desire some further assurance will be first the range of the signals and secondly their intelligibility. The official reports are very explicit on both particulars. And here I must explain that Mr Mance being on service in the Bombay Presidency brought his invention as early as 1869 to the notice of the Government of India who submitted it to every form of practical test. In a letter dated 16th April 1873 Colonel Roberts CB., VC Quartermaster-General writes “I am directed by the Right Honorable the Commander in Chief to submit for the information of Government a printed copy of a memorandum embodying the results of the several experiments and trials which have been made to test the efficiency of the heliograph invented by Mr Mance as a means of signalling for military purposes. The Commander in Chief is satisfied that the instrument even in its present form” (it has been vastly improved since then) “would under certain circumstances and where the electric telegraph is not available prove of great value in the field, and His Excellency is of opinion that six or eight heliographs should be made and stored up with the field telegraph train at Roorkee, some men of the sappers and miners being kept constantly practised in the use of the instrument,” and while “His Excellency does not consider the heliograph would be substituted for flags,” he observes, that “it is an instrument adapted for a special end and as such is extremely valuable.” With respect to the two questions of range and distinctness the memorandum above referred to says “All the reports agree in the following points (a) that the signals given by it are perfectly clear and satisfactory; and (b) that they can be easily read in ordinary weather without telescopes up to 50 miles.” The capabilities of the heliograph are therefore thoroughly established. My desire this evening is to draw attention to the subject of sun flashing generally and to show how well its study will repay Officers especially those on foreign service by whom the heliograph can be made available not only in cases of emergency to which they are always exposed but in their every day life. I am informed that a Staff Officer at Poona who had a country house about twenty miles distant used when there to go by appointment at a fixed hour to a certain window to receive and reply to messages flashed to him from Poona and so conducted his official business. This is but one illustration of the adaptation of the instrument to daily requirements it is not difficult to divine the thousand and one purposes it might be made to serve at a detached Indian hill station by uniting it with surrounding stations and the plains. But to return to the memorandum bearing the signature of Captain Collette D.A.Q.M.G.: “Messages can under favourable conditions be signalled distances up to 50, 80, or even 100 miles without using telescopes. Even during very hazy weather signals from Shaik Bodeen were quite distinct to the naked eye at Dehra Ismail Khan a distance of 38 miles, although the hill itself was barely visible. With telescopes and suitable mirrors (6 or 8 inches) there seems to be hardly any limit to the distance at which signalling could be carried on. A little consideration will convince us that the latter remark is no exaggeration. The sun’s light reaches us through say 92,000,000 miles, whether a million or two more or less the savans who recently observed the transit of Venus will perhaps shortly decide for us. Is it too much then to believe that after such a journey the rays preserve sufficient vital force to carry them a hundred or two miles further? Striking a mirror simply alters their course bends them to a new direction but makes little difference to their energy. We have a practical illustration of the fact in the moon which though not perhaps the best reflector projects the sun’s rays to us from a distance of 232,000 miles. The planet Neptune is three times the distance from the sun the earth is yet the solar rays reach it and are reflected back to us. Abundant illustration of the immense distance at which reflected light can be seen might be afforded from terrestrial objects but it is I feel unnecessary. The knowledge of the potency of sunlight as a signalling agent is at least as old as Alexander the Great whose fleet is said to have been guided along the Persian Gulf by mirrors during his invasion of India. I am informed on good authority that signalling by sun flashes is practised by the Indians on the North American prairies to this day; and the Russians had recourse to it during the siege of Sebastopol in 1854-5. But from Alexander of Macedon to Alexander of Russia little progress was made in this kind of telegraphy; indeed it had fallen into disuse, when, towards the close of last century, General Roy employed it in the operations he conducted to connect the meridians of Paris and Greenwich. Out of those measurements sprang the great trigonometrical survey of the United Kingdom, but recently completed. During the early periods of that survey it was customary to burn Bengal lights or Argand lamps at night on the distant points of which the bearings were required. The very limited range thus obtainable and other practical difficulties led that very ingenious officer Captain Drummond RE to an adaptation to survey work of what is now known as the lime light and so efficacious was it found that during the survey of Ireland in 1825 a range of 66 miles was obtained from Slievo Snaght in Donegal to Divis Mountain near Belfast. But a far more powerful agent than the Drummond light was about to be called into service. The manner in which General Roy employed reflection is not recorded but in 1822-3 Colonel Colby RE who was then conducting the survey devised a sun flashing instrument which though exceedingly primitive was attended with much success. It consisted of a stout plank on the face of which was nailed one below the other several plates of polished tin at angles calculated to reflect the sun’s rays for a considerable time in the same direction notwithstanding his apparent movement. The idea of sun flashing being thus revived Captain Drummond’s inventive powers were brought to bear and he succeeded in producing an instrument far more effective for the purpose than Colonel Colby’s tin plates. Taking a plain mirror as a reflector he devised means for adjusting it to any position and by a combination of telescopes of directing the flash truly. This highly ingenious but delicate and complex instrument he called a heliostat. Its power was marvellous; the Surveying Officers were enabled by its means to make their observations at three times the distance they could previously with much greater ease and with far less liability to error. It was soon found possible to reduce the complexity of the instrument the telescopes were dispensed with and other modifications made until it assumed the form it has ever since retained which though comparatively simple still requires an expert with a theodolite to direct it. How far these modifications were influenced by the heliostat invented about the same time by Professor Gauss and employed by him in the survey of Hanover, I am unable to say ; but what the heliostat then became it has ever since remained. Its function is to throw a steady flash of light between distant points to enable surveyors to take their relative bearing and for this purpose it has been in constant use in all great trigonometrical surveys throughout the world. The map issued to illustrate the survey of the United Kingdom shows the hundreds of triangulations which were made by means of the heliostat in the course of that operation. Many of the points of observation are from 60 to 100 miles apart and in the case of the triangle formed by Scaw Fell in Cumberland Slieve Donard in Ireland and Snowdon in Wales, the sides are 111, 108, and 102 miles respectively. This fact is worth bearing in mind in connection with the range of sun flashes in northern latitudes. The heliostat is however in no sense a talking instrument it is neither designed nor employed for that purpose although the strong desire of facilitating operations by communicating with their distant colleagues has doubtlessly led surveyors occasionally to the expedient of making pre arranged signals to each other. The heliostat had been in use nearly half a century when the happy thought occurred to Mr Mance of converting rays of light which had previously been regarded in a signalling sense as entirely passive into active speaking agents. This he did by adapting to a mirror mounted somewhat similarly to the old heliostat a means of imparting to the reflections the character of pulsations of varied duration in accordance with the Morse code. In fact in furnishing his instrument with a finger key he gave it a tongue capable of distinct and effective utterance he also found it a language in which to speak the Morse code. As the celestial bodies have already been used as illustrations I may refer to them again. The difference between a heliostat and a heliograph is the same in principle as if the moon instead of the steady reflection she has hitherto given us were to make her light intermittent sending it at short weil defined intervals in deference to a sudden desire on the part of the man her occupant to communicate with sublunary mortals through the medium of the Morse code. The heliograph is however as applicable to all forms of survey work as the heliostat besides being adapted to verbal intercourse. Whether the means adopted by Mr Mance for directing the flash of a mirror and converting it into articulate language is the best that can be employed time will show. Other forms will doubtlessly be attempted with which other names may be associated. It is seldom that an invention springs into life absolutely perfect. It is due to Mr Mance therefore to call attention to the fact that until the appearance of the heliograph no effective speaking sun flashing instrument was known to the world. In proof of this it is only necessary to refer to the important crises which have passed without its employment. To take a recent example If the heliograph had been in use in the French Army during the siege of Metz it would have been possible for Marshal Bazaine to have kept up communication with the Armies in the field operating for his relief despite all the efforts of the besiegers and had this been done it is certain that whatever other fate may have befallen France she would at least have been spared the disaster at Sedan. In case of siege the heliograph possesses one marked advantage over the electric telegraph. The latter is certain to be rendered inoperative at once by the destruction of the wires. The heliograph is liable to no such interruption. The limit of its range is dependent only on the elevation at which it can be placed It can signal to any and every spot round the compass in succession over the heads of the besiegers who are not only powerless to intercept it but might not be conscious of its existence as the flashes cannot be seen a little distance from the true line. It may be observed too that signals can be sent into a besieged city as easily as out of it a result not obtainable by pigeons and balloons. The heliographic conditions were not so favourable at Paris as at Metz but if communication could have been established between the city and General Chanzy when he approached so near to it with the Army of the Loire it is next to certain the siege would have been raised. Again during the Sepoy mutiny what a consolation would it have been to the devoted garrison of Lucknow to have been informed of the approach of the gallant Army which ultimately fought its way to its relief and also to that Army to have known how long the garrison could hold out. The mutual assurance could have been given by the heliograph with ease In fact a much simpler instrument than the hebograph would have sufficed. The requisite flashes could have been sent by an ordinary hand mirror as they could also have been sent at Metz and Paris. But the thought of converting the sun’s rays into speaking messengers had not then been born. It was much easier to find a hero like Kavanagh ready to risk the most horrible of deaths in making his way through the myriads of relentless foes surrounding the city than to call into existence a new mechanical agency. Next to the invention of the hebograph itself the most important service rendered by Mr Mance has been the persistency with which he has advocated the use of sun flashing in connection with the Morse code until at length the attention of the Indian Government and of signalling Officers generally has been thoroughly roused and in new emergencies it will not I feel assured be forgotten. But without looking farther into the past for illustrations which every Officer who has been on active duty will be able to supply I may refer to the vital importance that would attach to the hebograph in case of another mutiny or general uprising of the population in India. The first attempt of the insurgents would be a general cutting of wires and tearing up of rails throughout the country. The fighting value of the comparatively few British forces scattered over India depends in no small measure on the existence of easy means of communication between the different military stations thus knitting the detached corps together giving them timely warning of danger and common action against their enemies. With telegraphs destroyed and garrisons besieged unanimity of action would be impossible. Over such a vast area as India flag signalling can be of little value but a well developed heliograph system would preserve to the forces an inalienable power of holding rapid communication from one end of the country to the other. I need not say that the instrument which could ensure this in such a crisis would be priceless and the possibility of the contingency arising would in itself seem to justify the training of the signalling corps at home and abroad in its use. The value of the heliograph is however by no means confined to great and rare emergencies. The tripod instrument before you which weighs with cases and stand complete but 5 lbs has been constructed with special reference to ordinary service in the field. It is of great importance says Sir Garnet Wolseley in the Soldier’s Handbook that outposts should be able to communicate by signals with the main body and that officers in charge of patrols, reconnoitring or flanking parties advanced or rear guards should have the power of rapidly communicating with the General what they observe or the intelligence they may obtain. The question to be determined is whether the heliograph does or does not afford additional facilities for securing that communication on the importance of which Sir Garnet insists. I use the word additional advisedly. There is no desire whatever to depreciate or displace any of the signalling agents at present employed. On the contrary great pains have been taken to render the heliograph so light, handy, and portable, and so little subject to damage, that it may be added to the present signalling equipment without being felt as an incumbrance. The possibility of its extraordinary powers being called into requisition might be thought to justify its being taken into the field on all occasions but if the conditions were not favourable the signalling means at present employed could still be used. There are circumstances under which none of the existing systems are applicable yet which the heliograph would meet. It may be well however to say here a few words respecting the radical defects of sun flashing and of visual signalling generally. What is the good it may be asked of expatiating on the merits of an instrument the use of which depends entirely on the presence of the sun. In England sometimes the sun does not shine for weeks together and when it does just at the moment a signal should be made a cloud would possibly obscure it or some intervening object prevent the flash from reaching its destination. To such objections I would reply that the heliograph is not put forward as an independent or perfect signalling instrument. The telegraph though by far the most valuable of all signalling agents is far from being perfect. The electric telegraph is constantly liable to interruptions in war writes the distinguished authority before quoted and I may venture to add it is costly in money and men to produce transport lay and protect when down. Hence and because it can only signal in the direction of the wires its use in the field is very circumscribed being employed in none of the operations before mentioned as the objects of signalling. It is essential therefore as Sir Garnet proceeds to point out to hare the power of supplementing it and the utility of flags is warmly dwelt upon by him. But neither are they perfect. Flags are limited in range slow and laborious in manipulation they can be used only in specially selected positions they are exposed to the observation of foes as well as friends and in large operations are confusing from their number they also require special atmospheric conditions and the absence of intervening obstacles. Indeed free range one of the two requirements of the heliograph is obviously essential to every form of visual signalling and if the second viz favourable atmospheric conditions be not also existent flags and similar devices are of but little use. Thus in rain snow and fog they are on a par with the heliograph and in dull English weather it is questionable if much advantage attends them owing to the limited range attainable. The objections to tho heliograph apply more or less therefore to every form of visual signalling but it is scarcely fair to urge that because it is not adapted to the English climate it is not suited to English wants. The training and equipment of the Army is not directed exclusively against invasion. It is a long time since a foreign foe set foot on our shores and it will probably be a long time ere one does again. Our fighting has been done chiefly where there is no lack of sunshine in India China Africa and similar climes in which the objections to the heliograph lose all their force. Allowing therefore that practice with the instrument may be attended with difficulty at home no such difficulty exists where the Army is likely to be actively employed and where about half of it is permanently stationed. It cannot be presumed that the training of the forces abroad is not as important as of those at home It has already been observed that in combination with infinite disadvantages the heliograph is when compared with it in one or two respects superior to the electric telegraph. In comparison with flags it excels in range speed ease of manipulation secrecy less liability to confusion and the capability of making itself seen. This last quality is I think deserving of special consideration. I understand that if flag signallers are not placed with great care their motions cannot be discerned while the flash from a heliograph at once commands attention. It is not necessary to choose for it a position against the sky line or any particular kind of back ground the signaller may be quite hidden and not more than his general whereabouts known ; his station may even be completely obscured by haze or mist, but the moment the flash of his instrument is truly directed it is strikingly visible. It is on this account not less than on its great range that it is believed to be so well adapted to assist in securing that communication between patrols reconnoitring and flanking parties which is manifestly of such great importance. To further illustrate its possible use in field operations, if you will kindly pardon the evident want of strategy, and grant an eastern instead of an English climate. I will suppose an army lying in the neighbourhood of Sydenham for the protection of London from an invader advancing from the south coast and that reconnoitring parties have been sent to occupy at intervals the line of hills from Sevenoaks to Epsom Downs. It is probable that not one of those parties would lose five minutes in making itself known and establishing communication with head quarters. And further should the necessity arise for issuing new orders to the advanced parties no longer time need be occupied in finding them out. The construction of the instrument is admirably suited to the accomplishment of such purpose. Pressing the tangent screw out of contact with the wheel the mirror would be revolved slowly by the hand across the arc in which it was probable the out party was. This being done twice or thrice at one elevation of the mirror a turn of the vertical rod would admit of the process being repeated at another elevation till by gradual changes every inch of ground had been searched and the outpost discovered. This power of establishing communication being admitted I would submit whether the heliograph may not be found occasionally of much service to mounted reconnaissance parties. As conducted at present if the party happens to fall into the hands of the enemy the whole object of the expedition is lost. But if any member of it carried a heliograph as intelligence was obtained it would be flashed back to head quarters and thus not only would valuable time be gained but if any misfortune subsequently befel the party the loss would be mitigated as its purpose would have been served. It will be observed that the only essential parts of the instrument the mirror and adjustments are removable they weigh 1 1/2 lbs and by making the carbine or lance of a mounted man serve as a stand in the same way as the instrument has been fitted to a walking stick for the use of travellers that would be the only additional weight imposed. But by folding the tripod legs the instrument ready mounted may be carried in front of the saddle without inconvenience. It is made in any of these forms by Messrs. Elliott Brothers, Strand. The official memorandum I have before alluded to thus sums up the military value of the instrument as then discovered :- “On the whole it appears to me that while the heliograph will never supersede or be substituted for flags it may with great ad vantage supplement them flags are so easily made so portable and so efficient for the ordinary signalling required at the outposts &c of an Army that nothing better can probably be devised but it is exactly where flags fail that the heliograph will be found useful. In India we cannot I fear expect to have telegraphic apparatus always at hand and it is where a telegraph line would be so valuable that three or four heliographs might be worth their weight in gold viz to connect a force operating in the hills or elsewhere with the nearest electric telegraph station. For instance during the Umbeyla campaign a heliograph on the Crag Picquet and another at Permoulie would have been found very useful and in Abyssinia where for want of wire the electric telegraph stopped at Antalo a few heliographs would have extended the means of almost instantaneous communication up to the walls of Magdala. As it was mounted orderlies had to be used to convey messages along this part of the line. The adaptation of sun flashing to maritime affairs ought not to be altogether overlooked. It might be employed from lighthouses and headlands along the coast in defensive operations in coast guard service and for reporting the passing and arrival of vessels. Under favourable circumstances too I think it not impossible that directions could be flashed from the shore to boats and shipping at considerable distances and if so a wider scope would be given to it. But to whatever extent the heliograph may bo employed in military and naval operations it is I think as a substitute for telegraphic communication in the ordinary affairs of life that it will be most appreciated. In many tropical countries where the laying and preservation of wires would bo unremunerative the heliograph is calculated to afford to the inhabitants most of the advantages of an electric telegraph both as a means of internal communication and to join them to distant commercial centres. It is not many years since the most civilised countries had to depend entirely on visual telegraphy. Many of my hearers will remember when semaphores were in universal use and esteem. The heliograph is infinitely superior to the semaphore and in tropical countries its ability falls little short of an electric wire inasmuch as besides being available throughout the day by the application of artificial light it can be used also at night when both position and light being constant one adjustment of the instrument is sufficient. With moonlight also it is very efficacious. In commercial cities to which telegraphs have not as yet been largely applied it may be employed instead of the expensive underground and aerial wires. In countries where trunk lines only are laid the heliograph will act as a feeder bringing outlying parts into communication. It may further be employed in establishing communication along the frontiers and coasts of a country and in an infinity of other ways to which I need not allude. Remembering that I am addressing a military audience I have confined my remarks chiefly to the military uses of the instrument and if I have succeeded in awakening attention to the subject of sun flashing generally and to the heliograph as a means of utilising it I feel assured that it will be found a beneficent agent in emergencies yet unthought of.

Mr Gheaves: Some years ago I came across a volume of Galton’s Notes of Travel in which he describes how the North American Indians speedily availed themselves of this principle. They had found out the use of a mirror and from a lofty range of mountains through gaps in the forest they had made use of a piece of glass to flash many miles across the country a signal of their intentions and ideas to another body of Indians in ambuscade at a distance. That was the most primitive use I have found of this principle The Plain of Canterbury in the middle island of New Zealand extends some two millions of acres straight across to the mountains and I have often noticed the position of a house on the mountains simply by the rays of the evening sun striking on the panes of glass. I was at that time doing duty as a warden of the Trinity Board and the idea suggested itself to me that the principle might be applied to our lighthouses. We have a lighthouse at the entranco of Port Lyttleton in Canterbury at an elevation of 480 feet and the idea suggested itself to me that the men in charge of the lighthouse by this method might communicate with ships in the oiling and pilot boats by day or by night by day with the light of the sun by night with the artificial light and in reading the Year Book of facts I found that a flag staff that had been erected in Kew Gardens of a great height was finished with a glass diamond cut in facets at the top and that from these facets the rays of the sun could be seen at great distances in the neighbouring counties. I think that the whole argument speaks for itself. It is the simplicity of nature and it is so valuable that it is a wonder to me how it has remained in abeyance so long and has not been utilized. Extract from a letter in the Times of July 16th 1855 from Charles Babbage the Philosopher author of the Calculating Machine 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 Balakiava Timet July 11th. “A long train of provisions came into Sehastopol to day and the mirror telegraph which works by flashes from a mound over the Belbeck was exceed ingly busy all the forenoon. This can scarcely apply to any other than an occulting telegraph.” Extracted from Good Words, 1873, in an article on Lighthouses of the Future by Sir William Thomson LL. D., F.R.S.

Lt-Colonel Wilkinson 16th Lancers: Will you allow me to say a word or two? The remarks that have been made at present this evening on this subject have been in favour of this invention and having used it myself for the last two years, I feel bound to say that there are some points to be raised against it. Nature is constantly cutting off your line of communication. A passing cloud is quite enough to interrupt the most important message there is no means at hand to restore communication and at the critical moment of a battle your whole plans are disarranged by a cloud over the sun. This is an evil of such great magnitude that it at once places sun signalling in the second class. Besides this even a shower of rain will interrupt it and when we remember that in India which is our best field for this very instrument operations are usually if possible conducted in the cold weather when it is not at all unusual to have cloudy skies the instrument is frequently for days of no use. There is one thing in its favour which has not been urged this evening namely that it can be used at night with the full moon which gives very clear and most pleasant signals visible without the use of any glasses for a considerable number of miles one argument in its favour that of being seen at very great distances is modified by the fact that there are few places where you can see a great distance. Instance the valley of the Thames where could you see any object three or four miles away let alone forty? The difficulty is at once brought home to any one who practically attempts to use this instrument and even in India the solar haze is so great and so dense in the middle of the day that the flash is completely obscured at long distances unless sent from very high ground. This solar haze is such a practical difficulty in the use of either the heliostat or the heliograph that it becomes another reason why this instrument could not be universally trusted. The particular instrument before us has in my opinion and in the opinion of many who have adopted this system of signalling been far surpassed by an invention of Captain Begbie of the Madras Engineers. He and I and others who have used the instrument as at present presented to you have noticed that the action of the thumb on the lever has a tendency to alter the position of the glass. You must remember your tripod is standing probably on sand or gravel and the constant pressure of the thumb would cause the mirror to slightly move thus creating the long and short flash has a tendency to alter the position of the whole instrument. This is another fatal objection to the instrument as at present represented. Another is that the stall on which you take your aim at the distant station is so slender that in practice it is difficult to detect the flash on it. Captain Begbie’s system has a circular rim of metal with cross wires from it and where the wires intersect each other in the centre of this circle there is a small hole through which you accurately sight the distant station. This can be done with such extraordinary precision that you can have no sort of doubt about the distant station seeing your flash if you can see it clearly. He then places a screen on a separate tripod immediately in front of the mirror. By a pressure of the thumb the screen is raised or depressed and the screen rising in front of the mirror completely obscures the flash without in auy way moving the tripod on which the mirror rests therefore you may be perfectly certain if your mirror is adjusted that your distant station can see it and that the prossure of your thumb has not altered the direction. Another great thing against this invention is that the earth is constantly moving and the readjustment is most vexatious you have to be constantly readjusting the mirror as the earth revolves. Therefore unless you are prepared without the slightest danger of losing your position to gradually correct the angle at which the sun mirror is you are certain soon to find your distant station giving the vexatious reply repeat which means that they have missed your signal. Another objection is that if the sun is rising and you wish to signal to the west you are quite unable to do so. Captain Begbie has met this by a most admirable plan which once used is found to be invaluable. He has two mirrors if the sun is rising he places one to meet it and throws the light from that one on to the signalling mirror and by that he gets the full rays of the sun’s surface. One other thing deserves attention with regard to this subject and that is artificial light ; that, I believe to be the coming agent to supersede telegraphs and everything else for short distances. 1. With a strong powerful lamp used not exactly as this instrument is used but simply put in a conspicuous position screened in a way that the enemy cannot see it laterally or from below you can then signal with the greatest ease without any fear of detection and for the whole night without a single readjustment. You place a lamp we will say on a table you are in an upper storey and place your table so far back that you are sure tho rays of light will not reach the ground near you but they go straight forward to the distant station. You place a screen in front of the lamp which is worked by your thumb In that way you can sit through the whole night or as long as your lamp is burning it can be seen probably ten miles a good ordinary powerful Kerosene lamp can be seen for ten miles. I have signalled myself with a little 2 1/2 lb lantern for three miles with the greatest ease and without the use of glasses with a powerful lamp I believe ten miles could easily be done and that is really almost as much as is practically required. With lamps nothing can interrupt you no clouds can come in the way. Very few nights in India are there any fogs the fogs usually come on towards the morning but at any rate whether cloudy or clear you can use a lamp I have known times in India when we have been for three weeks or a month without a single day in which it is worth while to send out parties five or six miles for the purpose of trying the heliostat because we are almost sure we should be interrupted by clouds and that is a very great drawback. By the use of the lamp at night a party having been engaged as an outpost party all day from an Army advancing in the field and having individually collected important information can assemble together and from the highest available point can pass back to head quarters the information so collected. This may be done by a lamp, the best lamp in the village they need not always carry one with them but the best lamp in the village put on a common table with a screen in front of it will ensure their signalling bock ten miles with the greatest ease and with no fear of interruption A single cloud over the sun will interrupt communication by means of the heliograph and the worst of it is if it is too much relied on you are not prepared with anything to take its place therefore the interests of the Army may suffer seriously in the field.

Mr Goode: I am very glad to have found so able a coadjutor in the gentleman who has just sat down inasmuch as many of the points to which he has referred will be found in the paper but I omitted them in reading on account of the lateness of the hour 2. With regard to Captain Begbie’s modification of Mr Mance’s instrument I think I am right in so describing it and in claiming for Mr Mance the credit of being the originator of the first practical means of talking by sun flashing I may say that Mr Mance being in India when this idea was first worked out by him he unreservedly put the apparatus into the possession of the Government of India by whom it was tried under various phases and circumstances. As a matter of course it got into the hands of the different signalling officers and I presume of Captain Begbie amongst the number who would naturally examine all the details of its construction and doubtlessly endeavour to improve them. The instrument is not expected to be absolutely perfect and it is quite possible that Captain Begbie’s modifications may be of advantage. Mr Mance’s idea has been to keep the apparatus as simple as possible and to confine it under ordinary circumstances to one instrument. This instrument weighs 5 lbs with cases complete and it can be made as light as 4 lbs. Captain Begbie’s weighs 12 lbs and being in two distinct parts requires two operators. As regards the adaptation of artificial light to the heliograph there is no doubt that the utility of the instrument can be vastly increased by that means but the time at my disposal would scarcely admit of my entering into it fully involving as it does the relative power of different lights and many details as to the best means of preserving the signals from undesired observation I have however mentioned that Captain Drummond’s lamp was used for 66 miles in Ireland. For my own part I find a magnesium light or a simple lime light most convenient and serviceable but an electric light at permanent stations might be more effective. The form of instrument to which I have chiefly directed your attention is intended for use in the field where the application of artificial light is not easy of accomplishment with the other instrument here before you which is constructed for permanent and semi permanent positions nothing could be simpler. With regard to the defects of sun flashing they are entered into to some extent in this paper. The heliograph is not put forward as an altogether independent means of signalling but as an auxiliary. If the troops were operating in a country where owing to the formation of the ground or want of sun it was not available they would simply fall back upon whatever signalling means they have at present. The instrument is made so light portable and inexpensive that even if opportunity did not occur for its use but little labour would have been wasted while if its extraordinary power should be called into requisition the results would fully compensate the trouble of carrying it. With respect to the solar haze the Indian reports speak specially as to the capability of the flashes to pierce any ordinary haze up to 15 miles in which respect it much excels any other visual signalling apparatus. The difficulty of flashing due north whan the sun is duo south is apparent only Mr Mance in his original instructions dated 1871 makes special mention of the use of a second mirror under such circumstances which instrument would also serve as a reserve in case of accident. It has been said there is some difficulty in getting the adjustment perfect owing to the apparent movement of the sun. I can only say that I find in the memorandum from the Quarter Master General’s Department this testimony. All the reports agree in the following points (a) that the signals given by the heliograph arc perfectly clear and satisfactory and (b), that they can easily be read in ordinary weather without telescopes up to 50 miles. And it is singular that the official reports should have been so unanimous in pronouncing the signals clear and satisfactory if they could not be directed truly as in that case they would not be seen. It is quite possible that with instruments made in India without Mr Mance’s supervision and with manipulators not very experienced in their use some such difficulty might arise. But if the alignment is once correctly made the signaller has only to see that the flash rises to the stud and if so it must bo visible A slight movement of the adjusting screws obviates the movement of the sun and this can be done without interruption to the signalling. I cannot assert that Captain Begbic’s modification is attended with no advantages over Mr Mance’s method but it is evident there are disadvantages too. I think you will see that it is simply a modification of it and that to Mr Mance is due the credit of having first utilized sun flashing as a speaking means.

The Chairman: We must feel very much indebted to Mr Goode for bringing this subject before us. The subject is certainly very interesting. As to the originating the plan of talking by reflections I think we have had one instance of its being very old. I happen to know another the case of Admiral Sheriff then Captain of the Port of Gibraltar and in 1835 he told me he used with a common looking glass to talk to his friends at Tangier continually. But these are all tentative things alter all the credit is due not so much for digging the rude ore of any invention but for perfecting it and bringing it to use practically for the nation. Though this instrument may not be perfect for close use in the field. I quite see that for distant use under certain circumstances it may be of the very greatest importance not perhaps as fulfilling all the communications requisite between armies and distant stations but as fulfilling a great many requirements of very great utility. At any rate I think we are all very much obliged to Mr Goode for having brought this before us.

1- I believe that the electric telegraph is the only safe way of signalling a long distance and is essential to the safety of an Army in the field. 2- Another paper had been read earlier in the evening the discussion of which occupied more than the allotted time. I therefore asked and obtained permission of the Chairman to omit certain portions of my paper which if they had been read would have anticipated many of Colonel Wilkinson’s criticisms. I may now be permitted to remark that however liable to interruption heliograph signalling may be the fact of communication being made possible at all where the electric telegraph and all other signalling means have failed is a fact of great importance although the capability may not be constant Colonel Wilkinson’s remarks bear almost exclusively on the use of the instrument in the field. The signalling authorities at home and in India concur however in the opinion that the chief value of the heliograph will be at permanent stations. When so used a basis other than sand or gravel will of course be made for it and the line of direction between the stations being once accurately ascertained and marked would always remain the same the instruments being fixed. Supposing then Mance’s Heliograph to be when in the field defective in the points named which in the face of the official reports and continued trials I cannot admit in permanent positions these defects could not possibly existe. As to the necessity of adjusting the mirror to the constantly chonging position of the sun that process is as incumbent on Captain Begbie as on Mr Mance if he did not observe it his apparatus would he of but little worth Colonel Wilkinson forgets to mention that the working of a screen through 90 degrees to cut off the flash is a much slower process than altering the inclination of a mirror say 2 degrees and also that two men are essential to the working of Captain Begbie’s method while one only is required by Mance’s. The working expenses of the former at fixed stations are thus doubled and the rate of transmission is much slower. It has been fully acknowledged by the Government of India that Mr Mance is the originator of the means by which talking by sun flashing is accomplished and if the little defects mentioned have been discovered in his apparatus they admit of a very simple remedy. Instead of applying it advantage has been taken to associate another name with the system and so to transfer from Mr Mance the credit which I think all must admit to be due to the inventor of the heliograph. SG.

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