[ 2 75 ] 
prelfure was applied again!! one of the fupporters, 
which being removed, it was carefully noted, whether 
the wire returned again to biffed! the mark. 
At every ftation (or mark) the telefcope was turn- 
ed two or three times after the mark was fixed in the 
line, to prove that the faid mark was truly fet. — In 
general, the dittances between the marks did not ex- 
ceed a mile, nor were they lefs than half a one. 
The telefcope magnified about 25 times. Three 
or four marks were always left handing, and on a little 
rifing ground they would all be feen in a right line, 
the vertical wire in the telefcope bifiedting their centers 
without fenfible error. 
The marks made ufe of in continuing the lines 
were concentrical circles of black and white, painted 
upon both fides of aboard 14 inches fquare. This 
board moved in mortices made in two pohs, which 
were drove into the ground $ and, when the center of 
the faid mark was brought, by means of fignals, into 
the line, it was fattened by wedges to the polls. 
By means of a plummet, a peg was driven into the 
ground, and a notch cut in it, under the center of the 
faid mark, in order to fecure the line. 
In the evening, when we left off, a mark was 
placed before, and two or three left behind us ; and 
in the morning the inftrument was again fet up in 
the fame place, to prove that the marks were nor 
moved. 
The tremouf of the air (caufed by the fun’s rays) 
was often very great ; and, to avoid any error that 
might arife from the fluttering of the marks, w r e in- 
termitted our operations fometimes for five or fix hours 
N n 2 ifi 
