VOL. XC.] PHILOSOPHICAL TRANSACTIONS. J87 



nearer to the light than it should be to make them perfectly equal, any of my friends 

 who happened to be present, would mistake the black for the white. 



XX. An Account of the Trigonometrical Survey, carried on in 1797* 1798, and 

 1799, by Order of Marquis Cornivallis, Master-General of the Ordnance. By 

 Capt. Wm. Mudge, F. R. S. Communicated by the Duke of Richmond, F. R. S. 

 p. 539. 



This is now one more of the reports on the national military survey of this 

 country, which has been carried on for many years, under the immediate and suc- 

 cessive conduct of General Roy, Colonel Williams, and Capt. (now Col.) Mudge, 

 of the Royal Artillery, and which is still continued under the direction of the same 

 Col. Mudge. 



The contents of the work now meeting the public eye, are important and 

 numerous: it is divided into sections. The 1st contains the calculations of the 

 sides of the principal and secondary triangles extended over the country in 1 797, 

 1798, and 1799; with an account of the measurement of a new base line on Sedge- 

 moor, and a short historical narrative of each year's operation. The 2d section 

 contains the computed latitudes and longitudes of those places, on the western 

 coast, intersected in 1795 and 179^, ana< also such others, since determined, as lie 

 conveniently situated to the newly- observed meridians. This section also contains 

 the directions of those meridians ; one on Black Down, in Dorsetshire; another on 

 Butterton Hill, in Devonshire ; and another on St. Agnes Beacon, in Cornwall. 

 Among the contents are also to be numbered the bearings, distances, &c. of the 

 stations and intersected objects, from the parallels and meridians. The 3d and last 

 section contains the triangles which have been carried over Essex, the western part 

 of Kent, and portions of the counties joining the former, Suffolk, and Hertfordshire. 

 It is with satisfaction stated, that Mr. Gardner, the chief draftsman, with his assist- 

 ants, had nearly completed the survey of this extensive tract, which, no doubt, like 

 the map of Kent, will be given to the public : the materials for these different sur- 

 veys are ample, and will be found in this section, which concludes with the altitudes 

 of the stations and mean refractions. 



Before advancing farther in the work, Col. M. entertained ideas of condensing all 

 the data in his possession, and distributing them in it ; but, when he found his 

 paper would, in that case, be too large for the Philos. Trans, he desisted, content- 

 ing himself with presenting little more than a moiety : it is, even now, he says, of 

 inconvenient magnitude, but he could not with propriety still further abridge it, 

 having in several instances rejected important matter. That he will therefore take 

 an early opportunity of compiling a 4th account, in which will be given the latitudes 

 and longitudes of those places, in Essex, Kent, &c. found in the last section. In 

 the former accounts of this survey, the conductors were particularly guarded in not 

 intermixing their contents with distances determined from numerous doubtful inter- 



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