788 PHILOSOPHICAL TRANSACTIONS. [ANNO 1800. 



sections ; and experience has hitherto not detected above 3 or 4 errors arising from 

 wrong bearings or misnomers. Previously indeed to the compilation of them, a 

 great part of the objects in Sussex, Hampshire, and the Isle of Wight, were verified 

 by Mr. Gardner, in process of an extensive survey, carried on by the order, and 

 performed for the service of the Board of Ordnance. This gentleman will also have 

 it in his power to detect any errors, if. such exist, in the names of places to the west- 

 ward ; as the Master General has been pleased to issue his directions for the survey 

 of Devonshire, and as much of Somersetshire and Cornwall as will square the work. 



The principal object proposed to be accomplished in the year 1797, was the deter- 

 mination of the directions of meridians at proper stations, in order to afford the 

 necessary data for computing the latitudes and longitudes of places intersected in 

 the surveys of 179 5 ana * 1796* From errors which are the result of computations 

 made on the supposition of the earth's surface being a plane, it was expedient that 

 new directions of meridians should be observed, when the operations are extended, 

 in eastern or western directions, over spaces of 60 miles from fixed meridians. The 

 distance from Dover to the Land's End being upwards of 300 miles, it becomes 

 necessary, on this principle, that 4 directions of meridians should be observed ; 

 which, with that of Greenwich, amounts to 6, dividing this space into 6 nearly 

 equal parts. Whatever might be the stations farther to the westward, which offer 

 as fit places for these observations, Dunnose in the Isle of Wight seemed highly 

 eligible, not only because it is removed the necessary distance from the meridian of 

 Greenwich, but also because it commands a most extensive view of the western 

 coast : therefore, as the direction of the meridian was observed on this station in 

 1793, it became necessary to fix on 3 other places only. In the selection of these 

 stations, it was wished to have found such as should lie nearly in the same parallel, 

 each intermediate one being visible from those east and west of it; by which means, 

 the differences of latitude between their respective parallels would be accurately de- 

 termined. When the party was at Dunnose, in the year 1793, a hill at a very 

 considerable distance, in a direction very nearly west, was seen just rising out of the 

 horizon. It then occurred that this spot would, at some future period, be a very 

 proper one for a station where a new direction of the meridian might be observed. 

 Experience, in the survey of 1795, led to the belief that this hill was actually Black 

 Down in Dorsetshire ; therefore it was determined that the operations should com- 

 mence at that station, and the event verified the truth of the suppositions. 



As the high land in the vicinity of Teignmouth, in Devonshire, cuts off all view 

 of the southern extremity of Dartmoor from Black Down, the necessary alternative 

 was, the firing of lights on some remote station, communicating with Butterton. 

 Rippin Tor was quickly discovered to be the most proper spot ; and that eminence 

 would, in every point of view, be a most eligible one for a new direction of the 

 meridian, if the hills in the middle of the moor were not considerably higher. It 

 was therefore chosen only with a view of being subservient to the purpose of finding 

 the latitude of Butterton. From Black Down, the party removed to Butterton; at 



