1831.] 
Indian Meridional Arc. 
345 
of Mudge’s latitudes exhibit discrepancies of 5", while the variation of his 
theodolite angles seldom exceeds a sixth of that quantity. Part of these errors may 
be due to the instrument, for it is doubtful whether the great dimensions of such 
telescopes, with their wooden frame work, gives them any real ad\ antage oi ei 
metal ones of more portability and compactness. Captain Everest, howeiei, detei 
mining to free the Indian arc, as far as possible, from the errors of catalogues, calcu- 
lations, and instruments, has commissioned from the first of English artists, Trough- 
ton, two three-feet circles of exactly similar construction: one Will he placed at 
each extremity of his measured meridional arc ; and the same stars, and any 
number of them, will be observed with the two instruments simultaneously for a 
sufficient period : nothing can promise greater perfection ol result than this simple 
plan, and the liberality of the Court of Directors in disregarding the small 
addition of expence, deserves the highest praise. 
1 art of the errors of the vertical angles are attributable to the attraction o 
mountainous masses upon the plumb-line of the instruments : this cause of irregu- 
larity has been experimentally investigated by Maskelyne, Hutton, andbyPlaj 
>n his survey of Schehallien in 1774. The correction in most cases was thought 
trivial enough to be omitted in Mudge’s survey, but Don Rodriguez in a ' ei *> a 
manner reconciled an anomaly which came out on the publication of tbe o on^ 
measurement, whereby the length of a degree seemed to decrease, instea o 
leasing, towards tbe pole, by proving that tbe local attraction of Aibun u 11 
' 1,l ' e influenced the latitude taken at that place to the large extent of fi'e se 
Captain Everest in bis account of tbe Indian survey gives a similar instance o i 
necessity of attending to this circumstance, which Colonel Lambton was inc^ 
|° disregard. The plumb-line of their zenith sector on approaching the ed^e o 
°fty table-land, north of the Taptl valley, was drawn perceptibly to t le noi t 
and vitiat ed the latitudes taken in the valley to the amount of a few seconds. 
Connected with the trigonometrical determination of the earth s figure, are ^ 
experiments made in various parts of the world upon the length of t ie „ j 
W»m, so much encouraged within the last few years by the ******£ ,1" r 
^ convertible pendulum. At Madras, and on a se- 
\ a Unsa ulout ), Mr. Goldingham has already provided us wit ^ fflade in the 
nes °f experiments on this subject, which agree more close y 1 ment 0 fthe 
Atlantic, with the other deductions of geodesy. To comp e similar to that 
n( h:in survey, a Kater’s pendulum with clock and a i uS trument has, we 
1Isp (l in the polar expeditions, has been supplied : and a ( 1 j g oin bay. A first series 
Understand, been also sent to the Company s astronomer ^ id(J ut the Surveyor 
of observations with this instrument lias already been be ma de acquainted. 
e neral’s office, with the results of which we hope in clue * j (TOnome trical operations, 
B efore concluding our brief and imperfect sketch o ° ment q{ tbe results of 
11 wight he expected that we should enter briefly * nt0 m 0 f our knowledge 
these vast undertakings, and tlieir influence upoi gt gj ,„ore brief, !or , 
re garding the exact shape of the world. But here " e 1 were not a fit place to 
e ' en Were we competent to the task, this elemental) tricial ,s of the day arc 
1Scuss the many subtle points upon which the us e> serie$0 { experime 
at variance. It has been found, that none of tbe those of the pendulum, 
e «ed towards the solution of the problem, ieU a perfect accord* 
meridional arc, and the perpendicular to the m ' d t h e earth to be an 
Ce with one another : and many have hcnce Mr Ivory |,hs howler 
e gular solid beyond the reach of mathematics a . eX pose the limits of uUl - t 
■ien up the question in the mode best calculate 
