203 
Notes on Earthquakes and Extraordinary Agitations of the 
Sea.* By R. EpMonps, Hsq. 
I stated many years since that extraordinary agitations of 
the sea and of inland lakes are probably produced by vertical 
earthquake-shocks acting on the waters perpendicularly to 
the plane or surface of the ground on which they rest. The 
effect of such a shock in the bed of a canal would be not only 
to drive the water from its sides towards the centre where it 
would rise into a long ridge, but also to drive the water from 
its higher towards its lower end. In this latter case the water, 
when its momentum ceased, would flow back to the higher end, 
where, rising probably to a higher level than it had before, it 
would dam back any stream gently entering there. All this was 
exemplified in the Surrey Canal on the day of the great earth- 
quake of Lisbon. That canal was 700 feet long and 58 broad. 
“The water at its higher end usually deepens from two to 
four feet, growing gradually deeper to the west end, where it 
deepens to about ten feet.” At and near the higher (eastern) 
end the ridge of water raised in the centre was about ninety 
feet long, and between two and three feet above the usual 
level. This ridge heeled northward, and flowed over the walk 
on the north side of the canal; on the water’s returning 
into the canal, another such ridge was raised in the middle 
which heeled southward, and flowed over the walk on the 
south side. During this second oscillation, the small stream 
at the higher end, which constantly flowed through the canal, 
was driven back thirty-six feet towards its source. This was 
consideredt as the effect of the second oscillation; but no 
oscillation from side to side could have increased the depth 
at the higher end where the stream entered. It was probably 
the second oscillation from end to end that dammed back the 
stream, for it must then have reached the higher end of the 
canal, and deepened the water there. The oscillations from 
end to end no doubt escaped observation on account of the 
tenfold more striking oscillations from side to side. 
* Read at the Meeting of the Royal Institution of Cornwall on the 10th of 
May 1861. 
t Philosophical Transactions, vol. xlix. p. 354. 
