338 
AECHDEACON PEATT ON THE CONSTITUTION 
fluid below, and if this contraction or expansion was different from that of the dry land, 
water would flow in or out of the ocean and disturb the exact equality of matter in any 
two vertical columns drawn down from the surface of the land and the water. Also, as 
the crust contracted and brought into play the prodigious force of compression, which 
would inevitably cause the crust to give way at the weakest part and produce anticlinal 
lines, crushing, sliding, and interpenetration, there would be a slight increase of mass 
in some parts on this account. From these and similar causes it is readily seen that, 
since the epoch when the crust ceased to be thin enough to adjust its own position 
according to varying circumstances, changes must have occurred which would modify 
the previous state of things. Still the result of these modifying causes must be but 
slight, compared with those large effects of the mountains and ocean and crust, which 
nearly compensate each other, and which suggest the hypothesis. Another cause arises 
from the calculation itself. It is necessary to assume some law of distribution of the 
mass, that the calculation may be possible. I assume that the deficiency or excess of 
matter is distributed uniformly to a depth bearing a fixed ratio to the height of the 
land or the depth of the ocean. The actual distribution most likely differs from this. 
But this is taken as an average. We must expect, for these reasons, to find that the 
hypothesis is not satisfied with exact precision. 
4. Colonel J. T. Walker, B.E., Superintendent of the Great Trigonometrical Survey 
of India, to whom I had communicated the formulae developed in this paper, has lately 
supplied me with information showing the results of the Pendulum Observations re- 
cently made along the Great Indian Arc of meridian and at other places, and has 
obligingly allowed me to make use of the data. While these observations have been 
going on I have looked forward with great interest to the results, as I felt persuaded 
that the observations would furnish me with the means of testing, in a new and inde- 
pendent way, the truth of my hypothesis regarding the constitution of the earth’s crust. 
It is the object of the present communication to show with what measure of success 
the test has been applied* *. 
moving exactly as the crust, the force producing precession would from this instant give the crust anew motion, 
which the fluid has not, and which it has not time to acquire before, in the next small portion of time, the crust 
has shifted again with the same twist. The amount of precession must therefore depend upon the moment of 
inertia during the time it is generated, and therefore upon the thickness of the crust and not at all upon the fluid. 
* Since the above was written, Colonel Walker has sent me a copy of a printed letter and Note on the Pen- 
dulum Observations, from which I extract the following remarks. “The observations at the five northernmost 
“ stations indicate that there is much probability that the density of the strata of the earth’s crust under and 
“ in the vicinity of the Himalayan mountains is less than that under the plains to the south, the deficiency 
“ increasing as the stations approach the Himalayas, and being greatest when they are north of the Siwaliks. 
“ On the other hand, the observations of the five southernmost stations show an increase of density in proceeding 
“ from the interior of the peninsula to the coast at Cape Comorin. Thus both groups of observations tend to 
“ confirm the hypothesis that there is a diminution of density in the strata of the earth’s crust under moun- 
“ tains and continents, and an increase of density under the bed of the ocean.” This is the hypothesis I pub- 
lished in 1864 : see Proceedings, No. 64. 
