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direction of General Mudge, taken part in every one of the great operations of the survey, the base on the Rhuddlan Marsh having also been measured within the period now under notice. The appointment of Lieutenant-Governor of the Royal Military Academy was conferred on General Mudge (then lieutenant-colonel) in July, 1809, and from that time the executive duties of the survey were principally performed by Captain Colby, though, from the want of a published account, it is not easy to trace accurately his movements. His military progress was as follows: first lieutenant, 6th May, 1802; second captain, 1st July, 1807; captain, 5th March, 1812.

In July, 1811, Lieutenant-Colonel Mudge addresses Captain Colby (from Brighton) at Brecon, and communicates to him doubts expressed by Captain Hurd, Hydrographer of the Admiralty, as to the longitudes and latitudes of some important coast points: "Ponder," he says, "the contents of his letter, and when you can speak decidedly on the question, let me hear from you. I think the latitudes and longitudes of the Smalls Lighthouse, and Gresholm Isle, as given in the account, are right; I have not a copy of the work by me, or I should perhaps be able to determine the matter myself. I think you told me, on one occasion, that Gresholm Isle was not rightly fixed by the triangles first given. It is of consequence that Captain Hurd should be either proved wrong, or that the errata he has discovered may be acknowledged to be such, and these errata put to rights;" an extract which proves

the important position then occupied by Captain Colby, and the early attention he had paid to the correctness of the survey work. At this time Lieutenant-Colonel Mudge appears, from his letters to Captain Colby, to have been much distressed by a delay on the part of the Master-General and the Board, in sanctioning the publication of the account of the survey by Mr. Faden, and it is not unlikely that the recollection of these difficulties subsequently operated on General Colby's mind in checking an inclination to renew the subject of publication.

Another source of anxiety was the inquiry of "the military commissioners," before whom Colonel Mudge was summoned in his double capacity of Lieutenant-Governor of the Royal Military Academy, and Superintendent of the Survey. In his letters of September 2nd and October 1st (1811), the general results of this examination are stated to have been favourable, as he observes, "I am certain they were impressed with an idea of the extreme accuracy of the work," though it would appear that he expected from the commissioners some strong animadversions "on the apparent magnitude of the sum" expended upon it. The total expense of the work, for the first twenty years, from 1790 to 1810, as stated by Colonel Mudge, was as follows :—

Triangulation ... £21,000 for the whole twenty years. Interior survey.. 25,347 from 1800 to end of 1810. Engraving 7,818 from 1801 to end of ditto.

......

Total ......£54,165

Or, if the average be taken upon the whole period, an annual expense of 2,2087.; and if the average be taken on the last ten years only, which is more correct, an annual expense of 4,4167.-a sum very different from that assigned by public rumour, an anonymous writer having published a statement that "the expenses of the survey had exceeded 10,0007. per annum !" In Colonel Mudge's letter of November 5th (1811), it is stated that an application had been made by the Quartermaster-General to have the plans drawn from the survey sent to the Horse Guards, to be there copied for the use of his department. This measure was advocated by the Duke of York, and it was afterwards arranged that the plans should be sent to the Horse Guards in parcels of four, five, and eight, in succession, until the whole had been copied, and that this arrangement should apply to the future maps as well as to those already finished. After the publication of the account of the survey, in 1811, it was determined to prolong the meridional line into Scotland, and the triangulation of the mountainous districts of that country opened out a new field for the display of those personal energies for which Captain Colby was so remarkable. On the 9th September, 1813, Colonel Mudge writes"I have now to beg you will send me, upon a sheet of paper, a sketch of your triangles, with your meridional line laid down thereon, telling me when you give up the business; and you will now hear with great satisfaction the probability of my returning with you to the north next spring, to

finish our operations, for my health is much restored, and though I write by the hand of another, yet I am in many respects better than I have been for some years;" and he closed this letter with the passage of grateful eulogium on the services of his assistant and friend, which has already been quoted. The mind of Colonel Mudge was at this time much harassed by the attacks of various critics, some of whom gave their names, and others wrote anonymously. The paper of Don Rodriguez may be said to have led the way in this attack, although a candid reader of the present day will, it is believed, find nothing in that paper but a fair expression of doubt as to the sufficiency of the evidence afforded by the zenith sector observations for the determination of a great physical question. At the time, on the contrary, it seems to have been considered and treated as a personal and invidious attack either on the superintendent of the survey, or on the survey itself; and this mistaken feeling is strongly manifested in the letter which has been here quoted, whilst directing the attention of Captain Colby to a critical essay in the "Edinbugh Review," ascribed to Professor Playfair, on Colonel Lambton's reports on the Indian Survey. It is refreshing to observe the calm and candid tone in which Playfair examines the subject, in reference to the meridional arc measured in England. He first gives the various lengths of a degree determined by Lambton, as deduced from parts of the general arc of about three degrees—

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Punnae and Putchapoliam 60473 9° 34' 44"

Punnae and Dodagoontah 60496 10
Punnae and Bomasundrum (60462 11
Punnae and Panghur

Mean of the two last

34 49

4 44 83

60469 11

.

60465-5 11

6 23.5

From a former measure

ment

60494 12 32 0

And then pointing out that the same anomalies appear in these results as had been noticed in the measurements both of France and England, and especially in those published by Colonel Mudge, he observes, that " such anomalies will probably always occur where contiguous parts of the same arc are compared with one another. The degree in the parallel of 11° 6' 23" is less than that in the parallel of 9° 34', a degree and a half further to the south. This is similar to what appears in the degree in England; and there is an instance of the same species of retrogradation, when the parts of the arc between Dunkirk and Formentaro are compared with one another. Some part of this irregularity, but certainly a very small one, may be ascribed to error of observation; the greatest part must, we think, be placed to account of the irregularity in the direction of gravity, arising from the irregularities at the surface or in the interior of the earth; the attraction of mountains, for example, or the local variations of density in the parts immediately

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