Trigonometrical Survey. 445 
the iron staunch eons, and were otherwise sufficiently clamped. 
The sides and roof were each composed of four-and-twenty 
frames, covered with painted canvas, any of which could be 
removed at pleasure ; and the whole was covered with a tent 
formed of strong materials. 
Having thus detailed, in as short a manner as possible, the 
heads of such particulars as it may be necessary the public 
should be acquainted with, it remains only to give some ac- 
count of the improvements in our great theodolite, before we 
narrate the progress made in the survey in the summer of the 
year 1792. 
art. 11. Account of the Improvements in the great Theodolite. 
Mr. Ramsden has considerably improved this instrument, 
which, in other respects, is of the same dimensions and con- 
struction as that made use of by General Roy, which has al- 
ready been described in the Philosophical Transactions. The 
construction of the microscopes render them very superior to 
those of that instrument ; as the means by which the image is 
proportioned to the required number of revolutions of the 
micrometer-screw, and also the mode of adjusting the wires to 
that image, are much facilitated. (See Phil. Trans. Vol. LXXX. 
p. 146.). For the first, there are three prongs proceeding from 
the cell which holds the object-glass ; these, after passing 
through slits in the small tube which constitutes the lower part 
of the microscope, are confined between two nuts which turn 
on this small tube, so that by turning the nuts, the object-lens 
is moved towards, or from, the divisions on the circle, as occa- 
sion may require. To adjust the wires in the micrometer to 
the image ; in the upper part of the body of the microscope 
MDCCXCV. 3 M 
