OF THE PLUMB-LINE IK INDIA. 
701 
out that if the attenuation extend down to between 600 and 1000 mile.s the ellintidtv 
would come out equal to the mean value. In this case the residual mountain attraction 
K cousi era e. us, then, it appears, that although the hypothesis of Deficiency of 
Matter, d ,t extend to no greater depth than 100 miles or so, will very much multiply 
the effect of the Himmalayas and the mountain-region beyond on the plumb-line, the 
lesult shows that in computmg the Indian Arc there is little ground for working with 
the mean ellipticity, as is done in the Great Trigonometrical Survey. 
1-5 Nor are the peculiarities of the Great Trigonometrical Survey explained by the 
hypothesis of Deficiency of Matter below. None of the pairs of errors in the astrono- 
mical amplitudes given in par. 14, nor any which can be interpolated, coincide with the 
rrors in the amplitudes detected by Colonel Eveekst in the Great ArC. According 
to him, ^tronomical observations make the amplitude of the arc Kaliana-Kalianpu? 
too sma lby5''-236, and that of the arc Kalianpur-Damargida too large by 3''-789 
This latter eiror indicates the existence of some local cause of disturbance in th’^ neigh- 
bourhood of Damargida. That such local causes may exist without the presence of so 
enormous a mass as that of the Himmalayas, I have shown in a Paper on rEngHsh 
Dfions of thit Pa ! For example, in the course of the cflcii- 
onlv abl 600 ^t' (P- “ ^he Table). A tabular mass 
delction ofT-m tT by forty-six, will cause a 
deflection of 3 172 a a station three miles from its longer side, and about one-third 
one end of it and two-thn-ds from the other end. Colonel Eveeest himself enters 
m o an e a orate calculation in his earlier quarto volume (of 1830) to find the local 
attraction at the Station Takal K'hera, which had been previously fiLl upon afonH 
n^hlTrandtr V bTlI:"^ was afterwards abandoned, notwithstanding 
h t , r, K T ^ “P°“ calculations in connexion with 
extenstftabk lan^co ““ an 
I'^OO r 1 commencmg as far as twenty miles off, and rising to only about 
1600 feet above the level of the station. Colonel Lambton had considered the table- 
d to be too distent to have any effect; but calculation proved the reverse. 
. n fact, as it appears to me, while the absolute necessity of attending, to local 
i1 rr " investigations I have given in this and my " 
cle 1 hopelessness of attaining to any certain results seems to be as 
lands Ld'deT bh “ mountain-masses and table- 
ands and deep neighbouring oceans which affect the vertical, and which can be calcu 
others of twh 
have no oower r c’^cept that they may exist and that we 
inv causes The ‘heir existence. Were it not for these disturb- 
Mtv T the P^rts even of the same arc ought to bring out its ellip- 
frcity (If the meridian ie elliptical) with considerable precision. The approximation can 
* See p. clxxyii of his 4to volume published in 1847 
MDCCCLIX. g jj. 
