gret that the name of General Roy must be now passed by, without any attempt to do justice to his memory further than this brief record of the labours of the earliest British geodesist may have contributed to that object. Associated with General Roy in all his operations was Mr. Isaac Dalby, of whom General Roy had the highest opinion, and this eminent mathematician, who became afterwards Professor of Mathematics to the Military College, was, as it were, a connecting link between the preceding and the successive stages of this great work. Nor ought the name of the Duke of Richmond to be here passed over without some testimony to his memory and merits. and merits. General Roy particularly acknowledged the attention the Duke always paid to his representations; and it is from him that the great work of a national survey obtained its earliest and most decided support. Taking, then, into consideration the encouragement he conferred on this peculiar branch of the Ordnance service-asserting, by so doing, the claims of ordnance officers to be looked upon as scientific men-the patience with which he investigated the now popular subject of national defences, and the personal attention he bestowed on all the military departments of the Ordnance, including the Royal Military Academy, it may be justly said that the Duke of Richmond stands in the first rank of Masters-General of the Ordnance.

After General Roy's death the subject of a survey seemed, for a time, to be overlooked; but the Duke

of Richmond being informed that Mr. Ramsden had constructed a second three-feet theodolite, and two 100-feet chains, of great excellency, recommended to the Government that they should be purchased, and the work renewed, and this recommendation was successful. The first operation was a remeasurement with the new chains of the base on Hounslow Heath, and the result of this second measurement commencing August 15th, and ending September 26th, 1791, differed only from that of the measurement with glass rods 23 inches in excess. The new chains differed from the original steel chain made for the Royal Society, and before described, in this, that instead of consisting of 100 links of 1 foot, they were composed of 40 links only, each link being a parallelopipedon, 2 feet long, and half an inch square-a construction of great strength, and less liable to be affected by small irregularities in the supporting troughs or coffers, than a chain consisting of short links. At this stage of the proceeding, that simple, but most essential requisite, a safe observatory tent, was devised and constructed at the Tower it was octagonal, and consisted primarily of an internal skeleton of eight iron pillars, bound together by oak braces, and supporting a roof consisting of eight rafters united together at the top, and clamped at the bottom to the iron pillars. The sides and roof were composed of frames covered with painted canvas, and the whole covered with a strong tent. This construction was afterwards slightly

modified, and then continued in use till the period of the Irish triangulation, when it was still further modified and improved. The spring waggon, which has always proved so effectual in the transport of the great instrument, and has tended so materially to preserve it from injury, was now invented and constructed. The stations having been selected by Captain Mudge and Mr. Dalby, the triangulation was extended, in the years 1792-93-94, southward to the Isle of Wight, and connected with the previous triangulation of Kent, so that the groundwork was laid for the survey of a most important section of the country, and data obtained for important philosophical deductions. The operations closed in 1794, with the measurement of a base of verification on Salisbury Plain. This base was measured with the steel chains, and was found to be 36574-4 feet long, the length, as obtained by triangulation from the Hounslow Heath Base, being 36574-3, exhibiting, therefore, a difference of little more than an inch in length of nearly seven miles. The direction of the meridian was determined at Dunnose and at Beachey; but it is unnecessary to enter on this occasion into the calculations of the length of a degree of a great circle perpendicular to the meridian, in the latitude of 50° 41', which were founded on these observations. The operations of these years were conducted by Lieutenant-Colonel Edward Williams, and Captain William Mudge, Royal Artillery, and Mr. Isaac Dalby, and the results published in the "Philoso

phical Transactions," in 1795. The same gentlemen continued to conduct the work, and in 1797 was published an account of the operations of 1795 and 1796. In these years the triangulation was continued westward, so as to embrace the whole southern and western coast, and means adopted to fill in the great triangulation by a minor triangulation, the angles of which were observed by a smaller theodolite, eighteen inches in diameter, constructed by Ramsden, on the same principles as the great three-feet theodolites he had before made. This latter instrument was therefore taken into Kent to complete the materials for the survey of that county, by Mr. Dalby, and Mr. Gardner, Chief Draughtsman in the Tower, who then commenced his connection with a work in which he long continued a most valuable assistant, whilst a series of triangles was observed with the great instrument, extending from the Isle of Thanet, in Kent, through the counties of Dorset, Devon, and Cornwall, to the Land's End, and even connecting the Scilly Isles with the mainland. The Marquis of Cornwallis was now Master-General of the Ordnance, and the work appears to have assumed the distinct character of a national survey. The name of Lieutenant-Colonel Williams does not appear in connection with it after the publication in "The Philosophical Transactions,” in 1797, of the results of these two years' operations. In this paper Dr. Maskelyne gives the demonstration of that practical rule for

reducing the observed angles to angles of the chords, which was so long used in the British survey. In 1800, Captain William Mudge, then chief director of the work, communicated, by order of the Duke of Richmond, an account of the triangulation and survey in the years 1797-98-99. In this paper it appears that the Ordnance map of Kent had then been published, that the survey of Essex, portions of Suffolk and Hertfordshire, Sussex, Hampshire, and the Isle of Wight, were, under the direction of Mr. Gardner, in a forward state, and that the MasterGeneral had directed the survey of Devonshire and such portions of Somersetshire and Cornwall as were necessary to square the work to be undertaken. Mr. Isaac Dalby, worn out with the fatigues of this arduous service, now retired, and was succeeded by Mr. Simon Woolcot. The Royal Society having lent to the Ordnance the great circular instrument, or theodolite, which had been used by General Roy, it was determined to use one of the great instruments in completing the triangulation necessary for the surveys thus ordered by the Master-General; and the other in carrying through the country the meridional line already commenced. In 1797, the operations were principally confined to the determination of the direction of the meridian by observations of the Pole Star, at Black Down, in Dorsetshire, Butterton, and St. Agnes' Beacon; and horizontal angles at a number of stations required to connect them with the meridian stations. The operations of