496 JOURNAL OF SCIENCE. 
11.30 p.m., the water began to rise faster than ever, and in 30 minutes’ 
had risen 4 inches; then it turned and fell nearly as fast as it had risen, 
and reached its lowest point in 1 hour 41 minutes, having fallen exactly 
6 inches. At Douglas House the night was fine and calm, without the 
sign of astorm. Yet it seems probable that a storm passed over the 
north end of the lake, and started the motion, which kept on at intervals 
of about two hours for 14 hours, the rise and fall gradually getting less. 
I was fortunate enough to be present and see so much of the record and 
the corresponding weather. You have no doubt noticed that one set of 
pulsations was started by a sudden fall, and the other by a sudden rise, 
in the lake, and that the impulse which caused the water to rise was 
greater than the other. Similar impulses have kept the lake in almost 
constant motion ever since, and when once under way, they will go on 
throughout a gale of wind with just as much regularity as in a calm. 
Ordinarily such a set of motions lasts 10 or 12 hours, decreasing 
gradually as if the friction of the water stopped it; but on several 
occasions they have kept on for days together. The most remarkable 
impulse yet recorded was on the 14th of April, when the water was 
remarkably still, and had been so during the 11th, 12th, and 13th. At 
ll am. on that day Mr. Glover, who has charge of the gauge, saw a 
thunderstorm coming down from the’north, and went into the recording- 
house to see its effect. The lake was rising fast, and in 30 minutes rose 
4 inches; as the storm passed overhead the rising ceased, and the lake 
at once began to fall, getting back to its previous level in 15 minutes; 
passing this point it fell 2 inches more—in all 6 inches—and then began 
to rise again, so starting a series of pulsations that lasted five days. 
Rain came with this storm, and on 14th and 15th measured by gauges 
at each end of the lake 1:10 inch rain fell, and this caused a rise of 14 
inches in the lake, which can be distinctly seen in the record as some- 
thing independent of the pulsations. With the rain there was a strong 
breeze of wind, and by the third day after the water had returned to 
its old level, all the rain having evaporated in three days. In each of 
the cases I have mentioned so far the impulse seems to have been given 
by a sudden storm breaking over the lake, but there are other instances 
in which the impulse was of a totally different character, and it seems 
as if a small force properly managed was made to do duty for a large 
one, just as we should set a heavy weight suspended by a string in 
motion by giving it first a little push, and then adding impulse at each 
swing. So the force, whatever it he which in these. cases acts on the 
water in the lake, gives it a little start and gradually gets it in motion. 
The best instance of this occurred on the afternoon of April 5th; at the 
time the lake was very quiet, and suddenly the water rose an inch, and 
fell again within 30 minutes; next time it rose an inch and a half, and — 
fell 2 inches in three-quarters of an hour; the next time it rose 2 inches 
and fell 3} inches in an hour; it then rose 3? inches in 40 minutes, and 
so started a series of pulsations which settled down to two-hour inter- 
vals, and lasted 20 hours. Usually the rise and fall take about equal 
times, but now and then the whole fall will take place in 14 or 15 
minutes and the corresponding rise take 116 minutes, and it is not 
very unusual to find one in a set of twice the period of the others, as. if 
one had been left out. In fact the variations in the conditions of 
vibration are very puzzling. With a view of finding out the most 
common period I have measured 54 of the best defined amongst those 
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