1830 .] 
Of the late Col. Lamb ton. 
79 
officers of the army the method of topographical surveying,— an acquirement, we 
may say, absolutely necessary to military men. He had the merit of stating his 
case in so clear and convincing a manner, that the intention to abolish the Survey 
was relinquished. Captain Lambton had also a warm friend and admirer in Mr. 
Andrew Scott, of the Madras Civil Service,— perhaps the man in India best qualified 
to appreciate his labours. He was first judge of the court of appeal, but, owing to 
his well known attainments, was generally consulted by the Government on all 
such questions as had any connection with science. His favorable opinion of Cap- 
tain Lambton, and the countenance he gave the Survey, were doubtless of great value 
in supporting it against the ill founded objections of the ignorant. To these names 
we may add those of Lords Minto and Hastings, from both of which noblemen he 
received that encouragement and support which their enlarged minds and well- 
known liberality entitled him to expect. 
On the 10th April, 1802, the work was commenced 1 by the measurement of a 
base line of 40006,4 feet, near Bangalore, in 12® 54' N. Latitude. This, it is well 
known, is an operation of the greatest delicacy, and requiring all the attention of the 
observer, — all the refinements of modern science ; inasmuch as it is the base or 
ground- work of the whole operation, wdiich, as that is, will be correct or otherwise. 
The first base line, measured with any thing like an approach to accuracy, that of 
Picard’s survey in France, was measuxed with wooden rods, painted to protect them 
from the changes attributable to valuation of the weather. De Lambre and 
Mechain again used rulers made of platina and copper, which were insensi- 
ble to ordinary changes of weather, and by their indications gave the elements 
of the correction for temperature. General Roy, in the English survey, began 
by using deal rods, but found them so variable, owing to atmospheric in- 
fluence, that be was induced to re-measure the base on Hounslow Heath with 
glass rods. The latter appai’atus, though accurate, was troublesome in use, and a 
steel chain, jointed like a watch-chain, which was found equally accurate and 
much more convenient, was substituted in the continuation of the English opera- 
tions. Captain Lambton also used a chain similar to that used in England, and 
with the same precautions. The chain was laid iu coffers or long boxes, supported 
on stout pickets driven into the ground, and their heads di’essed even by means 
of a telescope. At one end of the chain was the di*aw-post, to the head of which 
the hither end of the chain being fastened, could be moved a little backwards 
or forwards by means of a finger sci’evv. Near the handle of the chain, and at the 
point where its measuring length was supposed to commence, there was a brass 
scale, with divisions, which was fixed to the head of another picket, distinct both 
from the draw-post and from those supporting the coffers. This scale could, by 
means of a screw, be moved backwards and forwards on the head of the post till 
it coincided with the mark on the chain. A similar ari'angement was made at the 
other end, but the handle of the chain, instead of being firmly attached to the 
weigh post, as it is called, has a rope passing over a pulley ; and to this rope 
is appended a weight of 2Slbs. to keep the chain stretched. This arrange- 
ment, it is obvious, enables the measurer to move his chain backwards or for- 
wards with the greatest nicety, and when satisfied that it is correctly placed, to 
keep it there perfectly steady ; while by means of the registers he marks exactly 
the places of the two extremities of the chain. The chain is then taken forward, 
and the hither end being adjusted to the scale which had before marked the fore 
exxd, a new chain’s length is laid off, and so on till the base be finished. Thermo- 
meters are placed in the coffers to determine the temperature of the chain ; and the 
rate of expansion being previously determined by experiment, the necessaiy cor- 
rections may he made for the varying temperature of the measurement. The quan- 
tity of this correction had been found by Colonels Williams and Mudge, to be on 
100 feet ,0075 inch for every 1® of Fahrenheit ; but Captain Lambton, by some 
experiment, performed with the chain itself, in October 1800, found ,00725 2 , which 
quantity he applied as the correction of his measurement. Small as the above dif- 
ference may appear to be, it would yet occasion, on a base of seven miles, a dif- 
1 While waiting’ for the arrival of the instruments from England, Captain Lambton 
had, in the latter end of October, measured a base near Bangalore in 12® 54' N. Lati- 
tude, partly to serve as a base of verification, — partly for continuing the series to the 
Malabar Coast. The ground was such as to occasion many breaks in the line, and 
though carefully measured, it was afterwards deemed expedient, on finding that a line 
of equal length could be had without any impediment, to reject it altogether and to 
measure a new base, which was done in 1804. The real commencement ol the Survey 
was, therefore, as above stated. 
* As. Res, vol, viii. 
