158 Alternating Currents. [April, 
loose pieces of timber, or anchors lying on the deck, and 
even men standing on the deck, as will also presently be 
shown, would be jerked up to heights proportioned to the 
violence of the shock. Much of the basin of the lake, 
however, is not horizontal, but sloping from its shores. 
Therefore when the shock which had proceeded vertically 
up from the interior of the earth reached the inclined or 
sloping sides of the basin, it would not continue to proceed 
up through the incumbent water vertically or perpendicularly 
to the horizon, but perpendicularly to the inclined plane of 
the basin, whereby the surface water dashed off would be 
jerked towards the centre of the lake. What I have called 
an earthquake-shock is really, however, only a single vibra- 
tion of an earthquake-shock; for an earthquake-shock 
consists usually of a rapid succession of vibrations, sounding 
at sea ‘‘like the letting out of a cable,” and on land ‘‘likea 
waggon rushing over a paved road.” By such vibrations, 
therefore, from the sloping sides of the basin, even if there 
were only five or six in a second, and the shock lasted only 
30 seconds, a great heap of water would be raised. The 
first vibration would, as I have said, jerk the surface water 
towards the centre of the lake, and before this dashed off 
surface water had time to flow back to its place, fresh 
surfaces would be jerked in the same direction by succeeding 
vibrations, so that the successive surfaces, whilst being thus 
dashed off, would form a current towards the centre, to 
supply which an efflux from the shores would necessarily 
follow. This efflux would not cease until the vibrations 
ceased, and then the heaped-up waters would immediately 
flow back to the shores. The subsequent ebbings and 
flowings, like the oscillations of a pendulum, would continue 
until the equilibrium were restored. 
The extraordinary movements of the waters so often 
observed in the American lakes, though not always of the 
same description as the two in Lake Ontario above given, 
may all, I think, be accounted for by my hypothesis. For 
example, if the earthquake shock in the bed of the lake be 
very partial, and do not occur on its sloping sides, but only 
on shoals near its centre—say two hills, or two parallel 
ridges, with sides inclining down into the intermediate 
valley—then the waters driven from these opposite sides 
would meet over the valley and form a high wave, which 
might flow on to the shore and rush up without any previous 
efflux beyond that slight and momentary retirement of the 
water which always precedes the fall of a wave on the shore. 
I have said that a vertical shock proceeding from a 
