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sulting engineer to the Admiralty), and Lieut. Drummond (Under Secretary for Ireland at the time of his death), were associated with Major Colby in the observations of eleven stations, including the Islets Faira and Foula, as connecting links with the Shetland Islands; and it was after this season of extraordinary labour that Major Colby took part in the renewed observations in France. This second visit was the result of an application from the Royal Academy of Sciences, and Board of Longitude of Paris, to the Royal Society of London, expressing their desire that the operations for connecting the meridians of Paris and Greenwich should be repeated jointly by commissioners of both countries, nominated by the Royal Academy of Sciences, and Royal Society of London. Messrs. Arago and Matthieu were chosen on the part of the Royal Academy of Sciences, and Captain Colby and Captain Henry Kater on the part of the Royal Society; but though this expedition was not immediately connected with the ordinary operations of the survey the Duke of Wellington assisted it to the utmost, by attaching to it a party of Royal Artillery, and authorising the supply of tents, and every other necessary store. Captain Colby also took with him Mr. Gardiner, his former companion on the summits of so many mountains, and Captain Kater paid only a just tribute to the merits of one of the most efficient public servants which the survey ever had, when he said, that "to the talents, zeal, and exertion of that gentlemen, on various occasions of difficulty, they were much indebted." The original

stations of General Roy upon Fairlight Down, and near Folkstone Turnpike, which, as well as Dover Castle, had been connected with the stations on the French coast, at Blancnez and Montalembert, were not at first refound, and as the gun which marked the important station of Beachy Head had been removed, it was irrecoverably lost. The difficulty in refinding Fairlight station was the consequence of a change, since General Roy's time, in the position of the mill, the distance of which from the station, together with the angle between it and Fairlight church, had been given as means for verifying the site. Everyone who has been engaged in the troublesome operation of refinding stations after the lapse of many years, must have experienced difficulties of this kind, and have further ascertained how hopeless it is to seek aid under such circumstances, from the treacherous recollection of the inhabitants. A circular trace of the old mill revealed its former position at Fairlight, and when the centre of this trace had been adopted as the point of departure the station was found with such precision, that on digging under the theodolite, the wooden pipe by which General Roy had marked his station, made its appearance, at the depth of four feet. The writer of this memoir, having on several occasions been required to get over such difficulties, has met with many examples of the erratic character of mills, though unfortunately they did not always leave evidence equally tangible of their wanderings; and has been driven almost to despair when he has appealed to human testimony. As a preliminary

towards discovering the old signal staff at Holyhead, he sent for the man who for many years had been in exclusive charge of it, and was informed by him that it had stood "just at that spot, sir, where those stones are; why, sir, I watched it for many years, and saw it removed, and those stones were exactly at its foot." Who could doubt such precise information? more particularly as the place seemed a very fitting one! The theodolite was put up, but alas! all the angles were wild, and evidently pointed to a very different locality. It was gradually moved in this direction, and the angles began to improve, whilst the signal keeper kept loudly protesting that it was leaving the right spot. At length the angles became consistent, and on removing some of the surface stones, amidst the protestations of the keeper that it would be useless to do so, the butt-end of the old staff was found, and the unwilling keeper forced to admit his error. On another occasion, in Anglesey, the published description represented the station to have been on the highest point of the hill, but time and agricultural improvement had so changed the surface that two small adjacent peaks appeared instead of one, and they were so vexatiously similar in height, and fitness for the purpose, as to defy selection. Well, the first person who came up was the farmer who, for many years, had been tenant of the land, and he at once pointed out one of the peaks as the true site, declaring that he remembered well when the party was there, and a gentleman who had lost his left hand was constantly looking through a

glass. Such testimony was irresistible; but the telescope having been put up flatly contradicted it: then came a neighbouring gentleman who said he had frequently visited Captain Colby, and looked through the telescope, and, with even greater confidence, pointed to the other peak as the right one. The telescope was shifted accordingly, but, strange to say, it denied the truth of the squire's statement, just as decidedly as it had done that of the farmer. Here was a dilemma! falling between two stools and not another in sight to rest upon! In such a condition of perplexity it was natural to appeal to the experience of Colonel Colby, and from him was received the laconic reply:-"Never mind the testimony of any one; trust to your instrument." And in truth this advice, though conveyed in terms of characteristic brevity, was most wise; and by following it a spot was soon found where the angles perfectly harmonised with those of olden time, although the plough had worked so great an alteration in the relative condition of the surface.

In order to facilitate observing across the Channel, compound lenses, of Fresnel's construction, then new to the scientific world, were used and M. Matthieu, and Captain Mudge, put up the first one ever used in England at Fairlight. It was formed of numerous pieces of plano-convex lenses, arranged concentrically so as to form one compound lens, three feet in diameter, through which the light of the lamp, four inches in diameter, and composed of several rings of wick, was refracted. The light far

exceeded that of any of the British lighthouses, and appeared at forty-eight miles like a star of the first magnitude. This application of the lens led to its adoption for lighthouses in Great Britain, as Major Colby lost no time in communicating his opinion of its excellence and advantages to his friend, Robert Stevenson, the well-known engineer and constructor of the Bell Rock lighthouse, a rival structure to the chef-d'œuvre of Smeaton, the Eddystone lighthouse. Mr. Stevenson acknowledges the receipt of this description of the lens in his letter of the 15th of November, 1821:-"I was much obliged by the letter you sent me of the 1st inst., relative to the French lamp and lens. I wish you could put me in the way of getting a lens, as I would put it into Inch-Keith lighthouse for trial. It will answer for a revolving light; but having seen the Tour de Corduan I cannot well understand why they should use so many lenses of the description you mention. I had once an idea of communicating your letter to Dr. Brewster, when I was with him the other day; but I thought he might wish to make some use of it, and I was not sure how you might view this. I am sure you could not make a more interesting communication to the Doctor, either for the Journal or the Royal Society." The subsequent modification of the lens cannot be here noticed; in the hands of Mr. Stevenson they were soon and successfully applied, and he always continued to recognise the part which Major Colby had taken in promoting their introduction. Robert Stevenson died in July,

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