the Trigonometrical Operation . j 2 j 
polls, and thefe remaining firm and motionlefs, as being 
wholly unconnected with any other parts of the apparatus, 
the chain was then moved forward into the fecond fet of cof- 
fers, where the thermometers were alfo placed. In thfe mean 
time, the firft fet of coffers now vacated, with their polls, &c. 
were carried on and arranged in the front, for the meafure- 
ment of the fecond ioo feet; and fo on continually with the 
others in fucceffion. 
Art. V. Of the furvey of Romney Marfh previoujly to the 
meafurement of the Bafe. 
In the introduction to this Paper it has been mentioned, that 
the Duke of Richmond had permitted Lieut. Fiddes, of 
the Royal Engineers, to be employed in 1786 and 1787 in 
railing a plan of that part of the Marfh where, on examina- 
tion, it fhould be found, that the bafe of verification might 
be the beft executed. In juftice to that officer, I confider it as 
incumbent on me to fay, that it was impoffible for any perfon 
to fulfil the duties entrufted to him better than he did, either 
in the courfe of the furvey, or fubfequent meafurement of the 
bafe, whereof he alfo had the direction. The general inftruc- 
tions given to him were, that after having by a bafe of his 
own determined certain triangles in the neighbourhood of 
Dymchurch,. Ruckinge, and Romney, by way of foundation 
for his work, he fhould preferve Ruckinge as the point whereon 
the allignement of the great bafe was to be directed, and vary 
the pofition of that end next the fea-wall in fuch a manner as 
to meet with the feweft local ofaftru&ions to the meafurement: 
between the two extremities. By infpedtion of the plan Plate 
II. which comprehends a traft of country of two miles in 
breadth, one on each fide of the bafe line, it will be perceived, 
that 
