
Dejflexions of the Plumb-line in India. 293 
disputed, but when I suggested that a chain of excessive 
density underlay certain named places, I was using the word 
“excessive ” relatively to the surrounding portions of the 
Karth’s crust in India. It is a question therefore not so 
much? of the negative variation over India compared with 
Europe, as one of internal variations in India itself. 
The pendulum observations in India show, if for the 
moment we exclude considerations of height, that there is a 
greater excess of matter in the crust under the two stations 
of Usira and Kalianpur than under any one of the other 
twenty inland stations in India. Of these two stations, 
Kalianpur is the one and only station situated on the line of 
the supposed underground chain of excessive density. Now 
the position of this line was deduced from the results of 
Astronomical observations, which are affected by horizontal 
attractions only. I think it is a significant coincidence that 
the pendulum results should show a maximum value of vertical 
force at the one station situated on the line derived indepen- 
dently from astronomical observations. 
Mr. Fisher thinks that the significance of this coincidence 
is lessened by the fact, that the same maximum value of 
vertical force has been observed at one other station, Usira, 
as well as at Kalianpur. But Ido not think that the observa- 
tions at Usira tell so much against the existence of a chain 
as the observations at Kalianpur tell in favour of it. 
Pendulum observations show the excess or deficiency of 
matter in the crust immediately under the station, but they 
give no clue as to the length or breadth of the matter, in 
which the excess or deficiency occurs. The attraction of an 
infinitely extended plain of rock of 1000 feet thickness is 
1°56 ; if the plain of rock be limited in area to a circle of 
7 miles radius, the observing station being at the centre, its 
attraction is still 1°56. The distances apart of the Central 
Indian pendulum stations, given in Mr. Fisher’s list, are as 
follows :— 
Badgaon to Ahmadpur . . . . 200 miles. 
Ahmadpur to Kalianpur . . . . 36_,, 
Kalanpor to Pahargarh. : . . 57 ,, 
robsears to- Were (eae. a TAL 
ewe i Baie eee, EIA 
Average distance apart . . 112 miles. 
The fact that the vertical force of gravity is the same at 
Usira as at Kalianpur shows that the same amount of matter 
underlies each; but Usira may overlie a small island of 
excessive density, and Kalianpur may be situated over a long 
