246 J. T. Walker— On Indian Pendulum Observations. [Nov. 
The Secretary reported that the following had been made over to the 
Indian Museum, under the provisions of Section 12, Act XXII of 1876: 
(l) 3 small figures ; one stone, one bronze, and one copper. (2) A 
celt found by Caj)t. Badgley at Shillong in 1873. (3) Geological and other 
specimens collected by Lieut. Temple during the march of the Tal Chotiali 
Force between Kala Abdullah Khan and Lugari Barkhan. 
The Secretary laid before the Meeting a copy of the 1st Part of Moore 
and Ilewitson’s Descriptions of New Indian Lepidoptera, lately received 
from England, and stated that the Council had conveyed the thanks of 
the Society to Mr. A. Grote and Mr. Moore for the care and trouble they 
had taken in bringing out the work and plates. 
The following papers were read :— 
1. The Evidence afforded by the Indian Pendulum Observations on the 
Constitution of the Earth's Crust and on Geodesy ; being an Extract 
from the Preface to Vol. Y of the Account of the Operations of the 
Great Trigonometrical Survey.—By Major-General J. T. Walker, 
R. E., C. R., E. R. S., &C. 
The Great Meridional Arc in India, which was measured by Colonels 
Lambton and Everest, was long regarded as one of the most important of 
the several arcs which had been measured in various countries for the 
determination of the Figure of the Earth. But a paper by Archdeacon 
Pratt, which was published in the Philosophical Transactions of the Boyal 
Society for 1854, shewed that the astronomical determinations of the lati¬ 
tudes of the stations of the Indian Arc might be very materially influenced 
by deflections of the plumb-line, caused by the attraction of the Himalayan 
Mountains, and the high Table-lands included between the mountains, and 
extending beyond them into Tibet. Thus a short time after the publica¬ 
tion of this paper, Colonel Clarke, of the Ordnance Survey, while making 
the elaborate and very valuable investigation of the Figure of the Earth 
which is appended to the Account of the Principal Triangulation of the 
Ordnance Survey of Great Britain and Ireland, London, 1858, was driven 
to the conclusion — which is expressed in the last page of the volume — that 
the value of the Indian Arc had been considerably diminished since the in¬ 
vestigations of Archdeacon Pratt. 
But the several Sections of the Arc, though showing some indication 
of having been influenced by Himalayan attraction, did not appear to have 
been influenced to anything like the extent to which they should have been, 
considering the magnitudes of the attracting masses. Thus it was sug¬ 
gested, by Mr.—now Sir G. B.—Airy, that the disturbing forces must be 
counteracted by some compensatory disposition of the matter in the in- 
