Trigonometrical Survey. 58 1 
error in the heights, we have 792 — 97 -f y — 702 feet, for the 
height of Rook's Hill ; and 792 -f- 131 — — = 916 for that of 
Butser Hill. From those two determinations, the others in 
table 1. have been obtained (the stations to the westward of 
Dunnose excepted) by taking the mean of the heights as de- 
rived from different routes. Those distinguished by an aste- 
risk, were fpuri& by taking ~~ of the contained arc for re- 
fraction. 
The refractions at the end of table 2, obtained from the dip 
of the horizon, are very consistent ; each being nearly y~ of 
the contained arc. The following were the observations : 
At Leith Hill, on July 2, 1792, at 10 in the forenoon, the 
horizon of the sea through Shoreham Gap was depressed 30' 
6 ". At Rook's Hill about noon on Sept. 2, 1 792, the depression 
of the sea, in the direction of Chichester spire, was 25' 30". 
At Nine Barrow Down, about noon on April 11, 1794, in a 
south direction nearly, the depression was 24' 16". 
The axis of the telescope was about 5^ feet from the ground 
at each of those stations. 
Table 1. 
Stations. 
Ground above 
low water. 
Feet. 
Dunnose - 
792 
Rook's Hill 
702 
Butser Hill 
916 
Hind Head 
923 
Chanctonbury Ring 
814 
mdccxcv. 4 F 
. 
