ak tremendously, but if the sloping
surface be made of square stone put together with reasonable care
there is not the smallest tendency to unseat these stones. This is the
principle of construction of Plymouth Breakwater. In the 3rd
construction, the slope makes the sea to break tremendously, and then
it strikes the perpendicular face with the force of a battering ram:
and therefore in my opinion this is the worst construction of all. A
few face-stones may easily be dislodged, and then the sea entering
with this enormous force will speedily destroy the whole. This is the
form of the Cherbourg Digue.

From this you will gather that I have a full belief that Plymouth
Breakwater will last very long, and that the Digue of Cherbourg, at
least its upper wall, will not last long. The great bank will last a
good while, gradually suffering degradation, but still protecting the
Road pretty well.

I was assured by the officers residing on the Digue that the sea which
on breaking is thrown vertically upwards and then falls down upon the
pavement does sometimes push the stones about which are lying there
and which weigh three or four tons.

I saw some preparations for the foundations of the fort at the eastern
extremity of the Digue. One artificial stone of concrete measured
12'9" x 6'7" x 5'7", and was estimated to weigh 25000 kilogrammes.

CHAPTER VI.

AT GREENWICH OBSERVATORY--1846 TO 1856.

1846

"On Nov. 7th I proposed a change in the form of Estimates for the
Observatory. The original astronomical part was provided by the
Admiralty, and the new magnetical and meteorological part was provided
by the Treasury: and the whole Estimates and Accounts of the
Observatory never appeared in one public paper. I proposed that the
whole should be placed on the Navy Estimates, but the Admiralty
refused. I repeated this in subsequent years, with no success.
Meantime I always sent to the Admiralty a duplicate of my
Treasury Estimate with the proper Admiralty Estimate.--Stephenson's
Railway through the lower part of the Park, in tunnel about 850 feet
from the Observatory, was again brought forward. On Feb. 20th it was
put before me by the Government, and on March 9th I made experiments
at Kensal Green, specially on the effect of a tunnel: which I found to
be considerable in suppressing the tremors. On May 6th I made my
Report, generally favourable, sup