4 50 
The Account of a 
clamp. This precaution is very necessary when white lights 
are used, for should there be a mistake in reading off an angle, 
when several are taken from the same lamp as the permanent 
object, it sometimes may prove troublesome to rectify the error, 
without sending other white lights to the stations. We found 
that to be the case at Ditchling Beacon, when only one person 
happened to be at the instrument, and a reading was set down 
10" wrong. A similar circumstance occurred at Brightling. 
For these reasons, lamps are greatly preferable to white lights, 
when the distances are not too great. 
As the instrument was sometimes found to sink on the axis, 
which was partly owing to wear by the constant use of it, and 
the screws of the centre work loosening a little by the shaking 
of the carriage ; whenever it came to a new station, the op- 
posite points were examined ; and if it was found that the 
circle had fallen, which would be shown by the runs of the mi- 
crometers, it was raised a little, and the microscopes re-ad- 
justed. 
At the different stations, after the observations had been 
made, large stones, from a foot and a half to two feet square, 
were sunk in the ground, generally two feet under the surface, 
having a hole of an inch square made in each of them, whose 
centre was the precise point of the station. 
art iv. Angles taken in the Tear 1792. 
At Hanger Hill. 
Between 
Shooter's Hill and Banstead 
o 
// 
Mean. 
