80 
Biographical Sketch 
[March 
ferenre of nearly two feet, supposing the change of temperature to be 20°, which 
in India it might well be. Aud this may serve to give some idea of the nature of 
these operations and of the extreme nicety required. 
Besides the chain originally belonging to Dr. Dinwiddie, a second was ob- 
tained from England, exactly similar. Its length had been fixed in the tempera- 
ture of 50°. This chain was preserved as the standard, and to its indications 
were reduced all the measurements made with the other. The length of this 
standard chain was afterwards corrected for a trifling discrepancy detected by 
Captain Kater, when comparing standards at home, previously to establishing a 
uniform system of weights and measures. 
The next operation was to establish the triangles, and make the angular measure- 
ments. These, in the older surveys, had been effected by the employment of a qua- 
drant furnished with two telescopes, which by means of a proper mounting and 
stand, could be placed in the plane of the objects. But the quadrant has long given 
way, both in this particular work and in astronomical observations, to the full circle, 
which is free from several errors inherent in the former. The introduction of the 
circle naturally led the way to Mayer’s capital improvement, by the application of 
the repeating property ; and Borda having devised a very convenient form of instru- 
ment, it was used by De Lambre and Meehain in their survey. Tlie continental 
observers appear to have rated this instrument too high ; nor do we wonder at it, 
when we consider bow satisfactory in theory the principle of their construction is, 
and how independent it renders them of bad division. General Roy again, who 
thought lie might depend upon the skill of our artists to divide the limb of the 
instrument correctly, preferred one of a different construction. This was the 
great theodolite, a plate of which may be seen in Adam’s Graphical Essays. 
The theodolite has its principal circle in the plane of the horizon, and its te- 
principal 
lescope, like that of a transit instrument, fitted for describing verticals. The angles 
are, therefore, taken at once as fitted for calculation, and do not require reduction, 
as those observed with the French repeating circle, being in the plane of the objects 
and inclined to the horizon. This is certainly a great advantage. Another ad- 
vantage which the English observers secured, was that of placing the centre of the 
angular instrument, exactly over or under the centre of the signal observed from 
other stations — whereas in the French survey, it was almost always placed on one 
side, and in consequence the observed angles required a second reduction to bring 
them to what they would have been if observed at the centre of the station. Cap- 
tain Lambton, using a theodolite similar to that of the English survey, was generally 
guided in all respects by the example of the conductor's of it. 
In May 1801, 
nant Warren 
801, a base of verification of 30793,7 feet was measured by Lieute- 
n, Captain Lambton’s assistant, near Bangalore ; and though the dis- 
tance was 160 miles nearly, the computed and measured lengths of this base dif- 
fered only 3,7 inches, or about half an inch in a mile : a proof of the great care and, 
accuracy with which the work had been conducted. The series of triangles were 
continued across to the other coast, along a belt of country extending 2° in latitude, 
detecting several errors in the positions of very principal places, and°in the breadth 
of the peninsula one of about 40 miles. 
In the 10th volume Asiatic Researches will be found a list of the positions de- 
termined by tins senes of triangles, amounting to 256. It would lead us too far 
- “ intricate and technical discussions to explain his methods of calculation : suffice 
say, they were the same as those employed in the English survey, and included 
But as Snrnp flrtnltt’ -rrritl, rp 
into 
it to 
the consideration of the figure of the earth. 
„ ... , , - - fixing geographical positions, there 
was a meridional series, arranged and measured with every attention to accuracy 
and at certain points along this line, zenith distances were obs^ed fo^ie pur 
pose of determining the value of the celestial arc in degrees and mln^ while^e 
In 1801 and 1802, a series had been esta- 
triangles furnished the length in feet. 
blished on a meridian about thirty-five miles west of Madr id ti 66,1 *, • i‘ 
io 04 / zcn /;nioi f .i J c , , ot Lauras, and the arc which 
mono e *1 b0494 fathoms for the length of the decree in lat 1 0 ® w' and 
61059 tor tl.at ot the perpendicular l„ the meridian. Buftt 
Snt^Cn’ “ chosen. The aeries on this n.eri- 
base. In 1800 ?t w^ean-iedTl" r‘* on the Bandore 
series was after- 
tiou was measured. From' UiL^erip ^ oitld}eto ° r > where a base of veritica- 
latitude lz° 55 ' was found to be 60498 ° °* th f de S ree of the meridian in 
a to De b04ys ^thorns, and that of the perpendicular 
