MEETINGS OF SOCIETIES. 495. 
southern end. The instrument is essentially the same as the tide gauge 
referred to in the earlier portion of this paper: but it differs in giving 
four inches of paper to the foot of water, and only three inches in the 
day for the time scale, instead of 24 inches as in the tide gauge. The 
float also is of glass instead of copper. To ensure the stability of the 
base of this instrument six piles six inches in diameter were driven as 
far as possible into the lake, and then cut off three feet above the water ;. 
the tops were secured together by a strong frame covered with two-inch 
planking, and then strong diagonal bracing was fixed between the posts, 
which makes them into one compact frame quite strong enough to with- 
stand any waves or wind known on the lake. This stage is 6 feet 
square, and on the top of it a small iron house, 6 feet x 5 feet. was put 
up to cover the recording gauge. A hole was then cut through the 
floor, and the iron well for the float let down. This is 18 inches in 
diameter, and is bolted to the floor, and by cross-bracing to the posts 
below in the bottom of it, six holes, an inch in diameter were made; 
these allow the water to go in and out with sufficient freedom to show 
ordinary waves without knocking the float.about. The house is built 
at the end of the jetty in front of Douglas House, and is 60 feet from 
the shore, the water at that distance from the edge being only 4 feet 
deep. The work of erecting the instrument was completed on the after- 
noon of February 18th, and the pencil was put down on the paper to 
begin its curious record at 7 p.m. on that day. At the time the lake 
seemed calm asa millpond, and looking at its smooth surface no one 
would have dreamed that such changes were going on in it as began to 
reveal themselves so soon as the pencil touched the paper, and in two 
hours the pencil had recorded a rise and fall of about 2 inches. This is 
not a motion like the ordinary wind-made waves, which pass by in two 
or three seconds, but a slow and gradual rise, occupying an hour, and 
then a corresponding fall in about the same time, to do which a current 
must first have set from north to south for an hour, and then reversed ; 
and if we consider for a moment the force necessary to put a body of 
water 18 miles long, 5 wide, and 15 or 20 feet deep, in such motion, we 
shall get some idea of the magnitude of the forces at work. The record 
had not been going 24 hours when it became obvious that these periodic 
motions in the level of the water had a period of about two hours, and 
on the afternoon of the second day, a heavy thunderstorm passed over 
the south end of the lake, and threw a little light on the cause of the 
pulsations. The storm rain was very heavy and much of it must have 
run into the lake tending to raise the waters there. With the storm 
there came a violent squall of wind from the south, on to the south end 
of the Jake; in a few minutes great foam-crested waves could be seen in 
the middle, and the recording gauge at once showed what was the 
matter; the wind had blown the water away from the south end and 
reduced the general level 3 inches. In 10 minutes the squall was over, 
and the water began to recover its level, in doing which the current set 
towards the south end of the lake, and could be seen running past the 
jetty at the rate of about two miles per hour. But it did not stop 
when the old level was reached, the momentum carried it beyond that 
point, and raised the water up at the south end of the lake. Then it 
turned and ran back again, repeating this process time after time at 
intervals of about two hours, the rise and fall getting gradually less 
until in about eight hours the water was almost still, when suddenly, at 
