1831.] 
Indian Meridional Arc. 
341 
disadvantage of continual attacks of fever that Captain Everest pushed on the 
triangulation to Kulianpur, and determined the latitude of that place by an ample 
series of celestial observations. Dr. Voysey fell a victim to the climate in De- 
cember 1823, and his companion was finally compelled to quit the field a second 
time at Bhaorasa, lat. 24° 10', and take his departure to Europe; having previously 
completed the prolongation of -the measurement to a total length of 16 degrees. 
We need not advert rnofe particularly to the operations of this period, since an 
interesting account of the whole was given to the public during Captain Eveiest s 
sojourn in England. 
During his absence, the subordinate officers of the establishment were emp oye 
in extending a series of triangles westward, along the Vindachal mountains, 
Benares, Patna, and Calcutta, which has been completed within the last fewmont is, 
and the final operation of measuring a base of verification has, as oui 
readers are aware, already made considerable progress along the Bairacvj , 
a line admirably suited for such a purpose. . . 
Having now terminated our brief historical outline of geodetica P^ 
we may proceed to describe the process of executing a trigonometric. J’ 
a very cursory mention of the instruments usually employed t iere0 > 
enable us better to appreciate the merits and excellencies o t ie c ie 
destined to supersede them in the continuance of the Indian at . 
The principles of the whole operation may be stated in a very ew wo^ 
line of sufficient length (five or six miles) .s measure ' * ment is expanded 
accuracy, npon the surface of the earth ; secondly, th‘S of triang l es , the 
north and south, in the direction of some mendian ) . g three mea- 
sides of which can he readily calculated from the given base, ^ cxtrem j. 
sured angles. Thirdly. The arc of latitude, comprehen b 
ties of the expanded line is determined by the inclination of the vertica 
Bne, with regard to the fixed stars. . . whole work, its mea- 
I- As the measured base line is the foundation o ^ ^ jj ne should be as 
surement demands every possible accuracy ot execut^ half t he length 
long as the surface of the ground will allow; and mu st be permanently 
°f the average sides of the large triangles. The two ci ^ carr y the ad- 
established by sinking a mass of stone or metal int nlUS t also command 
justed points at the extremities of the line • tlC1 , ^ ie base should form a right 
a view of the first triangle stations, with two ot w 
nngle as nearly as possible. (PI- XXIII- fig- E t „ nces (about 100 miles apart 
There should be bases of verification at certain on diverging asil> c * rl 
to check any errors in the first, which would other S length 0 f the whole lm< - 
angulation proceeded ; being in fact a peicentag P measurements, wit 
Wooden rods or perches were employ ed on a w eatber : m th e * 1 rU ! * ^ oW , 
any precaution to shelter them from the action o The irregtil»"‘' n ' 
they were even occasionally suffered to oa on erc toog" ,a 
»er. produced hy humidity and change of temple- ^ 
notice long. General Roy found reason to ab !”^. t ,.ioo rf "'io - %£* 
and after an elaborate series of experiments on nl , pcH r to h "' e . K 
gave the preference to glass tubes of 2 ee tobe5 do not set m ^ fiun- 
their duty with extraordinary precision, the introducin' r „. e jefccU 
nsed in any other survey, having been ***** ; ^ 
hied foot steel chain, which had the » ™ U , e difficult ® ' , urc> and 
of the chain were, the wearing ot the g . its precise tc 1 
ways with equal force, the impossibility of know. g 
