38 On Local Attraction. [No. I, 
involving three unknown quantities. The asswmplion which I then 
make is, that the Mean Figure of the Earth is a spheroid; that is, 
that these three ellipses are all the same. The effect of this is to give 
me four equations of condition, involving the three unknown 
quantities. These I solve by the method of least squares. The result 
is that the unknown deflections all come out very small; and the 
semiaxes of the three ellipses come out remarkably near each other in 
value. The first part of this result shows, what I have intimated in 
para, 2, that the local attraction arising from invisible causes hidden 
in the solid erust of the earth must be such, as very nearly to 
compensate for the effect produced by visible causes at the surface 
existing in mountains and oceans. And the second part of the result 
gives a very satisfactory solution of the problem of the Mean Figure 
taking local attraction into account, making the semiaxes 
20926189 and 20855316 feet 
1 
295°3 
5. In the fourth or last section of the Paper I enter into specu- 
and the ellipticity = 
lations regarding the Constitution of the Earth’s Crust, suggested by 
the result of the preceding section. The following extract will best 
represent my views on this interesting subject :— 
“The first thing I observe in the results given in the last paragraph is — 
the very small amount of the resultant deflections at the two extremities of 
the Indian Are—Punne close to Cape Comorin, and Kaliana the nearest 
station to the Himalaya Mountains; whereas the effect of the Ocean and 
the Mountains has been shown to be very large. This shows that the effect 
of variations of density in the crust must be very great, in order to bring ~ 
about this near compensation. In fact the density of the crust beneath the 
mountains must be less than that below the plains, and still less than that 
below the ocean-bed. If solidification from the fluid state commenced at 
the surface, the amount of contraction in the solid parts beneath the 
mountain-region has been less than in the parts beneath the sea. In fact, 
it is this unequal contraction which appears to have caused the hollows in 
the external surface which have become the basins into which the waters 
have flowed to form the ocean. As the waters flowed into the hollows thus 
created, the pressure on the ocean-bed would be increased, and the crust, so 
long as it was sufficiently thin to be influenced by hydrostatic principles of 
floatation, would so adjust itself that the pressure on any couche de niveaw 


