242 PHILOSOPHICAL TRANSACTIONS. [aNNO 1787. 



that part of Kent. The right hand stations occupy in general the heights 

 which extend across the Wealds. Those on the left are placed on the great range 

 of chalk hills, which end on our side of the Channel, between Folkstone and 

 Walmer Castle, and recommence on the opposite side between Cape Blancnez 

 and Calais. I do not mean to make St. Paul's a station in the suite; because in 

 that case Harrow and Hampstead must also have been used, all 3 extremely in- 

 convenient for the reception of the great instrument. Besides, Greenwich Ob- 

 servatory being hidden from the country to the south-west by the Norwood 

 heights, and from that to the south-east by Shooter' s-hill, after having made the 

 detour of Harrow and Hampstead, and come across the srrioke of the Capital, 

 we should still have been obliged to make use of the 2 stations of Norwood and 

 Shooter's-hill, without procuring so good an intersection of Bottle-hill, or Bot- 

 ley-hill, as is obtained by means of the station at the Hundred-acre-house. But 

 though none of the stations of the series actually fall within London, yet from 

 those in its vicinity, viz. the Pagoda, • Norwood, Greenwich Observatory, and 

 Shooter's-hill, we shall equally have it in our power to determine accurately the 

 situations of Harrow, Hampstead, and St. Paul's, as well as manv other chief 

 steeples within the limits of the Capital. Another principle I have endeavx)ured 

 to adhere to, in the disposition of the triangles, is this, that, after having ob- 

 tained sides in length from 12 to 18 miles, I continue them at that length as 

 much as the circumstances will permit; for, if they came to be reduced consi- 

 derably below that extent, the obvious advantages of a long base at the outset 

 would be lost, by the subsequent contraction towards the close of the operation. 



The tower of Tenterden church, being a very conspicuous object, may be 

 seen every where from the summit of the chalk hills, as far west as the river 

 Medway. It may also be seen from the eastern extremity of the second base, 

 by which the last triangle, Tenterden, Lid, Allington Knoll, is proposed to be 

 verified. This knoll is itself a very remarkable object, more accessible, and in 

 other respects more proper too for the purpose of a station, than Lymne church 

 steeple, which I had at one time thoughts of occupying. The high ground 

 which separates Romney-marsh from the Wealds of Kent, passes immediately 

 behind Ruckinge, that is, to the north-westward of it, and may therefore pro- 

 bably prevent the top of the chalk hills from being seen from the west end of 

 the base of verification ; but if Tatterlees-Barn, or any other point on the range 

 near it, can be seen from Ruckinge, then the station on the knoll, as well as 

 that at Lymne, will become equally unnecessary, and the triangle of verification 

 will become Tenterden, Lid, Tatterlees. 



I propose to have a station on Fairlight Head, a land of considerable height, 

 whence there is a good view of the coast of France near Boulogne. From this 

 point and Tatterlees, with the help of the Indian lights^ I have no doubt of ob- 



