250 J. T. Walker —On Indian Pendulum Observations. [Nov. 
tions, by Dr. Young’s rule. Thus the ratio of gravity at the extreme 
stations of Minicoy and More would not be very sensibly altered from what 
the given vibration-numbers indicate ; but the increase in the vibration- 
number would gradually diminish in passing from either of the two extreme 
stations to any intermediate inland station, which is situated too far from 
the sea to be influenced by its density, and on land too low to raise the 
sea-level sensibly ; consequently the ratio of gravity at the central as com¬ 
pared with the extreme stations may be very sensibly affected, that is to 
say by the amount due to an alteration of 2 to 4 vibrations at one or other 
of a pair of stations under comparison. 
Still, however, making every allowance for these causes, the broad fact 
remains that the observations at the Indian pendulum stations exhibit a 
marked increase of gravity, when we proceed from the interior of the conti¬ 
nent to the coast and then to the islands of the ocean ; and they also indi¬ 
cate a very marked decrease, when we proceed towards and ascend the high 
table-lands of the Himalayas. These facts point to a condensation of the 
matter of the earth’s crust under ocean-beds, and an attenuation of the 
matter under mountain-beds, the crust contracting and condensing wher¬ 
ever it sank into hollows, and expanding and attenuating wherever it rose 
into continents, as has been suggested by Archdeacon Pratt. 
This seems a fitting place for giving a brief sketch of the Archdeacon’s 
labours and investigations, on the subject of the effects of Himalayan 
Attraction upon the Geodetic Operations of the Great Trigonometrical Sur¬ 
vey of India. 
The question was first brought to his attention, in 1852, by the then 
Surveyor General, Sir Andrew Waugh. Discrepancies of 5"’2 and 3"-8 
respectively had been met with between the computed and observed am¬ 
plitudes, in the two northernmost sections of the Great Arc, Damargida- 
Kalianpur-Kaliana, the observed value being in defect in the northern and 
in excess in the southern section. They were supposed to be due to the 
influence of the groat mountain range to the north, though distant fully 
sixty miles from Kaliana, the nearest of the three stations. Archdeacon 
Pratt set himself to calculate the actual amount of the attraction of the 
Himalayan mass, and of the deflection on the plumb-line which it would 
cause at the three stations. The result obtained was very much larger than 
bad been expected, or than was required to explain the differences between 
the astronomical and tke geodetic amplitudes. The Archdeacon’s calcula¬ 
tions were communicated to the Royal Society, in the paper already alluded 
to which was published in the Philosophical Transactions for 1854. This 
paper is followed by one by G. B. Airy, Esq., Astronomer Royal, suggest- 
