594 
AECHDEACON PEATT ON THE INDIAN AEG OF MEEIDIAN. 
Everest. Some other cause must exist tending to increase the upper astronomical 
amplitude by 13"'ll — 5'''24=7"‘87, and also to increase the lower amplitude by 
3"-82-|-3"-79 = 7"-61. 
(6) It has been demonstrated that a slight but wide-spread variation in the density 
of the crust from that deduced from the fluid-theory, either in excess or defect, such as 
there is no difficulty in conceiving to exist, is sufficient to account for deflections such 
as these. For example, an excess of density amounting only to -^th part, extending 
through a circuit of about 120 miles around the mid-point of the whole arc between 
Kaliana and Damargida (and therefore not far from Kalianpur), and to a depth of 
about 200 miles, will produce this effect, and make the calculated deflections from the 
three causes — the Mountains, the Ocean, and this tiidden Cause below — exactly accord 
with the observed errors in the astronomical amplitudes. 
(7) The resulting total deflections at Kaliana, Kalianpur, and Damargida, arising 
from the three causes, are 26"'29, 21"‘05, and 24"‘84: these make the two astronomical 
amplitudes, the one 5"‘24 smaller, and the other 3"’79 larger than the geodetic ampli- 
tudes, the errors brought to light by Colonel Everest. 
(8) No sensible error can arise in the relative situation of places determined by 
geodetic measurements, and arranged in a map. But the position assigned to the map 
itself on the surface of the mean spheroid will be affected by local attraction ; viz. by 
the error at the station the latitude of which is observed in order to fix the map. This 
error may amount to as much as half a mile. Any station afterwards inserted in the 
map, from an observation of the sun, will be out of its place on the map, by the differ- 
ence of the errors arising from local attraction at that station and at the principal 
station which fixes the position of the map on the spheroid. The calculation shows 
that this error may amount in some places to as much as one-tenth of a mile. 
