VOL. LXXXV.] 



PHILOSOPHICAL TRANSACTIONS. 



657 



Stations. 



Ground above 

 low water. 

 Feet. 



Dunnose 7.92 



Rook's Hill 702 



Buiser Hill 916 



Hind Head 923 



Chanctonbury Ring 814 



Leilh Hill 993 



Ditchling Beacon 858 



Eeachy Head 56+ 



Fairlight Down 599 



Brightllng Down 646 



TABLE I. 



Ground abo\c 

 Stations. low water. 



Feet. 

 Crowborough Beacon .... 80+ 



Botley Hill 8j;0* 



Banstead 576 



Shooter's Hill 446 



Hanger Hill 230 



King's Arbour 118 



Hampton Poor-house S6 



St. Ann's Hill 240 



Bagshot Heath 463 



Ground above 

 Stations. low water. 



Feet. 



Dean Hill 539 



Beacon Hill 690 



Old Sarum 266 



Nine Barrow Down 642 



Highclere goO 



Wingreen 94.1 



Motteston Down 698* 



Bow Hill 702* 



Portsdown Hill 447* 



TABLE n. 



Mean refraction of 

 contained arc. 



Between 



Banstead and Shooter's Hill 



St. Ann's Hill and Hampton Poor-house 



Brightling and Beachy Head 



Beachy Head and Fairlight Down 



Dunnose and Butser Hill 



Highclere and Butser Hill 



Butser Hill and Hind Head 



Beachy Head and Chanctonbury Ring . 



Highclere and Hind Head 



Rook's Hill and Dunnose 



Leith Hill and Hind Head . . . 



Bagshot Heatli and St. Ann's Hill 



Dean Hill and Beacon Hill 



St. Ann's Hill and Banstead 



Dunnose and Nine Barrow Down 



Leith HUl and Crowborough Beacon . . . 



Rook's HiU and Hind Head 



Dunnose and Dean Hill . . . 



the 

 1 



• T 

 1 



• r 



• T 

 Jj_ 



• 1 o 



■ T5 



■ T5 



1 

 10 



1 1 



1 

 1 2 



1 



■ T? 



' I 2 



■ TT 



1 

 IT 



Mean refraction of 

 Between contained arc. 



Brightling and Fairlight Down . . 



Leith Hill and Chanctonbur)' Ring 



Leith Hill and Shooter's Hill ' 



Brightling and Crowborough Beacon 



Hanger HiU and Banstead 



Hanger Hill and St. Ann's Hill 



Leitli Hill and Banstead 



Beacon Hill and Wingreen .... 



Rook's Hill and Chanctonbury Ring 



Dean Hill and Wingreen 



Rook's Hill and Butser HiU 



Nine Barrow Down and Wingreen 



Leith Hill and Ditchling Beacon 



Mean of all the above, nearly 



Leith Hill and the Horizon 



Rook's Hill and die Horizon 



Nine Barrow Down and the Horizon 



th« 



TT 



1 



T7 



I 



Ti 

 I 



TT 

 TT 



1 



TT 



TV 

 1 



TT 

 I 



r? 



1 



1 



TT 



t 



33 



I 

 1 2 



I 



TS 



t'S 



I 

 ITS 



Remarks on the foregoing tables. — ^The height of the ground at the station on 

 St. Ann's Hill, table 1, is 240 feet; but according to General Roy (Philos. 

 Trans, vol. 80, p. 232) it is 321 feet: this very great disagreement however 

 principally arises from the variableness in the terrestrial refraction. In 1787, at 

 the station near Hampton Poor-house, the ground at St. Ann's Hill was elevated 

 17' 39"; but at the same station in 1792, when the axis of the instrument was 

 at the same height above the ground, the elevation was only 8' 11". General 

 Roy took -rV of the contained arc for the effect of refraction, and considered 

 the height of St. Ann's Hill, when deduced from that of the station near Hamp- 

 ton Poor-house, as more accurate than could be obtained by way of the station 

 at the Hundred Acres. But, before the survey in 1787, he found by the 

 barometer, that the station on St. Ann's Hill was 200 feet higher than the 

 Thames at Shepperton ; and he added 33 feet for the descent to low water at the 

 sea; the sum is 233 feet, agreeing nearly with our determination. 



We take the height of Botley Hill (89O feet) a mean of gOO,885,885, which 

 the observations at Leith Hill, Banstead, and Crowborough Beacon respectively 



VOL. XVII. 4 P 



