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Thomas Drummond (10 Oct 1797 - 15 Apr 1840) Scottish civil engineer who invented the Drummond light (similar to limelight) for night surveying, and attempted to adapt it for use in lighthouses. Short biography of Thomas Drummond >>

Drummond's Inventions

Drummond Light and Lighthouse Experiments

from Memoir of Thomas Drummond (1867)

Thomas Drummond

[p.81] ...Till the Spring of 1826, Mr Drummond remained invalided with his relations in Edinburgh. He was too weak for severe study; but he managed, notwithstanding, to effect a variety of improvements in his light apparatus, which he was bent on fitting for lighthouse use. In the spring he returned to London, where he was occupied during the summer and autumn in experiments for forming new measuring bars with which it was intended to measure the base at Lough Foyle. Late in the autumn he again took to the field. The station this year was Slieve Donard, in the County Down. Drummond joined the camp in October, and continued there till late in November. As in the previous year, the tempests were fearful, and must have grievously tried his already weakened condition. ...

[p.83] ...We now come to the operations of 1827 and 1828, and the inventions connected with the,. In these years, Mr Drummond was engaged in measuring the celebrated base of Lough Foyle—the most accurately measured base in the world, as Sir John Herschel assures me, except perhaps that measured by Maclear at the Cape by means of the same measuring apparatus. ...

[p.113] ...The anxiety and exposure attending the operations in 1828 had seriously affected his health—the second, if not the third time, that a severe illness had sprung out of his devotion to the service. He suffered much, as in the winter if 1825, from palpitation and sleeplessness. [p.114] He refers to this illness in a paper read before the Royal Society, June 17, 1830, “On the Illumination of Lighthouses.” The Trinity House Corporation had resolved, as early as 1826, to give his light a trial as soon as the apparatus should give a steady continuance of light, and be fit to be entrusted to ordinary attendants.” The survey of Ireland, however,” he says, “had just been commenced; and being employed on that service, I found it impossible to continue my experiments, in the first instance, from constant occupation and absence from London, and latterly, from & long and severe illness, the consequence of a very laborious and anxious duty in Ireland. During the last winter, however, I was again able to return to the subject.” The reference is to the measurement of the base, in the course of which he had suffered much from inclement weather, and from frequently standing in deep water (as in crossing the river), intent on the measurements, and regardless of himself.

This, as I have said, was the second, if not the third illness suffered in the service. Miss Drummond speaks of a severe illness, the date of which I am unable to fix. He occupied, she says, a hill-station in Ireland. The weather became tempestuous, and the station untenable; yet he held to his post at first from a sense of duty, but afterwards from inability to leave it. A chance visitor to the station, who happened to be a medical man, discovering his condition, hastened for assistance to the house of a landed proprietor in the neighbourhood. He described the camp hut as filled with water, and Drummond as certain to die if allowed to remain in it. The gentleman appealed to at once made for the hill, accompanied by his son. They found Drummond very ill, and had to carry him to the carriage, [p.115] where they rolled him in blankets which they had provided. Having taken him home, they nursed him with the greatest care and kindness, for the six weeks which passed before he was able to return to his mother's house. Miss Drummond's recollection is, that the name of these hospitable people was Mac Causland. She adds, “He was about a fortnight with us before he was able to go out just a little. I remember the Survey people wanted to stop his pay. He wrote them a thundering letter. ‘Was there ever anything equal to this?’ he said; ‘they throwaway thousands of pounds, and would rob me when I am become disabled in their service.’” He heard no more of the threat to “suspend payments.” It seems impossible that this account can refer to the illness which followed the sojourn on Slieve Snaght. Larcom thinks the time must have been the close of the first season at the Base.

He arrived in London late in the autumn of 1829, to prosecute his design of fitting the lime-light for lighthouse use. He had been engaged in improving the apparatus for this purpose in the spring of 1826, and may then have got it nearly into shape; he was certainly ready to bring it into use very soon after his return to town. Before the end of the year he was busy with experiments instituted by order of the Trinity House, for ascertaining the relative merits of the different methods of illumination in lighthouses. Some of these were carried on at the Trinity House; others at a small lighthouse at Purfleet, which had been placed at his disposal by the Corporation. They were conducted under the direction of the Committee for the Management of the Lighthouses, and they fairly established the superiority, at least in brilliancy; of the Drummond Light over all others.

[p.116] The original light apparatus had been designed for the Survey. Portability, rather than economy, had been studied in its construction. The ball of lime—from which when intensely ignited the light was derived—was heated by means of a stream of oxygen directed through a flame of spirit of wine. This source of heat was expensive, and, in considering the changes now to be made, economy was a primary object. For the alcohol Drummond substituted hydrogen gas, which proved not only much more economical, but productive of a considerable increase of brilliancy in the light.

The new apparatus was exceedingly ingenious. The oxygen and hydrogen gases, proceeding from separate gasometers, arrive at a small chamber, where they are made to mix. Into this chamber the oxygen gas is projected horizontally through a series of very small apertures, the hydrogen gas rising into it vertically through a series of similar apertures. From this the united gases pass through two or three pieces of wire gauze, and, being thoroughly mixed, issue through two jets against the lime ball in the focus of the reflector. To prevent the wasting of the ball opposite the two jets, and at the same time to diffuse the heat more equally, the ball is made by the apparatus to revolve once in a minute. Notwithstanding this movement, the heat cuts a deep grove in the ball, and it becomes necessary to replace it by a new one every three-quarters of an hour. As it would be unsafe in a lighthouse to intrust the replacing of the ball to an attendant, the apparatus is so contrived that it effects the replacement itself. The number of balls required to maintain the light for any time are placed on a. wire passing through the focus of the reflector; the ball in the focus drops the moment it is sufficiently worn, and its place [p.117] is instantly taken by another—the next above it on the wire—which two minutes before has fallen into a position to be gradually heated for doing duty in the focus.1

From a letter dated January 16, 1830, written to his sister, it appears that the Duke of Clarence, who a few months later became King William IV., had been expected to witness the experiments in his character of Master of the Trinity Corporation; and that an experiment which had been made with thc lime-light, before the apparatus had been brought into perfect working order, had resulted in an explosion. Miss Drummond had cautioned her brother not to enter upon the experiments till he had completed his preparations.

The Duke of Clarence was present, and highly gratified, when the lights were exhibited at the Trinity House on the 5th of March; after the exhibition he [p.119] presided at a dinner of the Corporation, to which Drummond went as a guest. By the month of May 1830 the scene of the experiments was transferred to the lighthouse at Purfleet. The light was making a sensation again, many of the most distinguished men in London going to witness its brilliant effects. Though Drummond did not oppose the experiments for testing the efficacy of the light at a distance, as that might have been impolitic, his view of them, expressed to his mother, was, that they were “mere trifling, and waste of time.” They were spreading his reputation, however, and every day bringing him new friends. By this time, six of his lights had been ordered by the East India Company, at the cost of L100 apiece. He was astonished at, but rather regretted, the Company's liberality, considering the hands into which the lights would fall. “I am busy,” he says, “preparing an account of our operations in Ireland, to be delivered as a lecture on Friday at the Royal Institution.”2 Friday was also to see the last of the experiments on the lights. “I will then present a report to the Trinity House, and they will decide what further steps should be taken. I am writing a paper on the experiments for the Royal Society.”3

This paper has been already referred to. It opens with a rapid history of methods of illuminating lighthouses, and account of those in use in the best lighthouses of Great Britain and France; a description, accompanied by illustrative plates, of the new apparatus [p.120] for exhibiting the Drummond light is next given, and is followed by a summary of the results of the Trinity House and Purfleet experiments.

The first set of the experiments were on the illuminating powers of the different lights, independently of the lenses or reflectors with which they are generally used. In these the method of shadows, and that of equally illuminated surfaces, both dependent on the same principle, but requiring different instruments, were employed. The standard used was an Argand lamp, 7/8 inch in diameter, supplied with the finest spermaceti oil, and capable of supporting a flame 1¾ inch in height. It was found that the light emitted by the French lamp, a large Argand, with four concentric wicks, was equal to ten standards; while that emitted by a lime-ball only 3/8 of an inch in diameter,. heated by two jets, was equal to thirteen standards. The next set of experiments respected the intensity or intrinsic brightness of the lights, the property on which their utility in lighthouses more immediately depends. The French lamp was found to be four times, while the lime-light was 264 times as intense as the standard! “These results,” says Mr Drummond, "were obtained by screening the lights, and then placing equal apertures opposite each, changing the apertures, and taking the mean to destroy the effect of any inaccuracy in size. The intensity of the lime-ball being, therefore, 264 times that of the Argand lamp, a single reflector, illuminated by the former, will be equal to 264 reflectors illuminated by the latter; but the divergence of the reflected light, depending on the size of the luminous body in the focus, will he smaller with the ball than with the lamp, in the proportion of about 3 to 8; hence, in such a lighthouse as that of Beachy Head, 8 reflectors may be [p.121] substituted for 30, and yet an effect would be produced 26 times greater than that of the present light, the most perfect of its kind in this country.”

By similar experiments, it was found that the French lens, a compound one, built up of separate pieces, on a principle first suggested by Sir David Brewster, was equal to 10·4 reflectors, taking into account the effect of the additional lenses and reflectors that ought to accompany it; and that the effect of a single reflector with a lime-ball would be equal to 25 times that of the French lens, accompanied by those additional lenses and reflectors.

“Such appear to be the singular and important results,” says Mr Drummond, “of our late experiments at the Trinity House. Made with every precaution by different individuals with different instruments, and unbiassed by the knowledge of each other's results, I see no reason to doubt their accuracy; and the comparative appearances of the different lights, when exhibited at a distance of ten miles, though not admitting of being reduced to numbers, confirm the striking superiority of this method of illumination."

The comparative appearances of the lights, as seen at a distance, are described in a letter, addressed to Mr Drummond by Captain Basil Hall. The lights were exhibited from the temporary lighthouse erected at Purfleet, and were observed from the Trinity Wharf, Blackwall, at a distance in a straight line of 10¼ miles. Drummond being engaged at Purfleet, could not himself judge of the effect. But among the observers were Sir George Cockburn and Mr Barrow from the Admiralty, accompanied by several naval officers of high standing; the Lord-Advocate of Scotland, Sir Thomas Brisbane, Colonel Colby, Captain Beaufort, hydrographer [p.122] to the Admiralty, and several others eminent for their professional and scientific attainments. Captain Hall assured Mr Drummond that he had endeavoured “to frame his account of what passed in strict conformity with the general sentiments of the party, and neither to exaggerate nor underrate any of the results.”

The superior brilliancy of the light being thus established, the only point for farther inquiry was the expense of its production. The result of Mr Drummond's inquiries on this point are set forth in his paper, and are unfavourable to his light. “It may, however, in this, as in every similar instance,” he observes, “be expected that, after a little experience, a considerable reduction in the cost would be effected.”

It was but for a short time that Mr Drummond was free to prosecute such inquiries. He was engaged in them up to the spring of 1831. In a letter to his mother, dated February 22, 1831, he writes: “Truly this same light gives no small trouble. . . . In the last paper which I sent to the Commissioners, I stated that the French light equals, if it does not surpass, the best of the lights in our lighthouses in splendour, while it is superior to them in economy and facility of management. This Stevenson either denies, or has hitherto been negligent in ascertaining. . . . The experiments at Inchkeith have been ordered by the Commissioners [of the Northern Lights], with a view to judge of the point themselves, and not trust to Stevenson's opinion. It is a question between the present method and the French light, not between mine and either. Their relative values have been ascertained by the Trinity House and Blackwall experiments, in a way which admits of no doubt. To recommence similar experiments would be mere trifling. There are obstacles in my way of a different kind, relating to the manufacture of the gas, management, &c., which I am now endeavouring to remove. With respect to brilliancy there can be no doubt." By the middle [p.127] of the year, however, his political employment commenced; and though he never lost sight of the subject, he was never able again to recur to it. “This abstraction of Mr Drummond's attention,” says General Larcom, “at the moment when he was nearest to success, must, so far as the light is concerned, be considered matter of regret: with its projector it has dropped; but if it be practicable, ingenuity will, doubtless, sooner or later, be directed to render it available, and the Drummond light may yet cheer the homebound mariner from the Great Skellig or the Tuakar."5....

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