Trigonometrical Survey . 457 
out that quivering motion, which, in summer, it generally has 
in the middle of the day. 
art. vi. Improvement in the Axis of the great Theodolite ; and 
the Progress o f the Survey in the Tear 1793. 
Towards the conclusion of the last year's operation, it was 
found that the axis of the instrument, by the frequent use of 
it, was considerably worn, and which was, perhaps, increased 
by the motipn of the carriage, as the arch could not be 
clamped with tightness sufficient to prevent the circle from 
moving within the limits of the bell-metal arms, and the up- 
right part of the travelling case. The consequence was, that 
it sometimes became necessary to let the circle lower by means 
of the screws 1 and as it was found to be exceedingly difficult 
to turn them equally, and by a quantity which was just suffi- 
cient, an application was made to Mr. Ramsden to apply 
something to the axis,, which might enable us to adjust the 
circle with greater ease and accuracy. Accordingly, upon the 
party arriving in town, the instrument was taken to his house, x 
and left there for the winter, during which he made the de- 
sired alteration. 
The progress made in the survey during the last season, 
determined the extent of the business for this year : and 
it was then imagined, that with good weather, we might be 
enabled to join the triangles to the eastward with those of 
General Roy, and likewise observe the remaining angles in 
the series, having first made the necessary observations at 
Dunnose and Beachy Head for obtaining the directions of 
the meridian. It had also been foreseen, that it would soon 
become necessary to select some spot for the measurement 
