236 
NATURE 
[Fuly 9, 1885 
came a violent squall of wind from the south, on to the south end 
of the lake ; 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 sud- 
denly, at I1.30 p.m., the water began to rise faster than 
ever, and in 30 minutes had risen 4 inches; it then turned 
and fell nearly as fast as it had risen, and reached its 
lowest point in I hour 41 minutes, having fallen exactly 6 
inches. At Douglas House the night was fine and calm, 
without the sign of a storm. 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 cor- 
responding 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 Io 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 remark- 
ably still, and had been so during the 11th, 12th, and 13th. At 
I1a.m. 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 the 14th and 15th measured by gauges at 
each end of the lake 1°1o inch rain fell, and this caused a rise of 
14 inches in the lake, which can be distinctly seen in the record 
as something 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 im- 
pulses seem 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 be, 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 after- 
noon of April 5, 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 34 inches in an hour; it then rose 32 inches in 
40 minutes, and so started a series of pulsations which settled 
down to two-hour intervals, and lasted twenty 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 corre- 
sponding rise takes 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 
already recorded. Of these 33 have a period of 2 hours 11 
minutes, five a period of 2 hours 5 minutes, six a period of 2 
hours 17 minutes, and ten a period of 1 hour 12 minutes. The 
periods of those on the Lake of Geneva are 72 minutes and 35 
minutes. Of those in Lake George which have a period of 2 
hours It minutes, some are the largest yet recorded, and others 
only a half or a quarter of an inch rise and fall; so that there 
must be something which makes or tends to make the period 2 
hours 11 minutes. It is noteworthy that at Lake George as 
well as the Lake of Geneva, the short seich is not half the long 
one ; but they bear about the same proportion one to the other 
ineach case. As to the cause of these motions in the lake I am 
not prepared to say much at present. Further investigation is 
needed, and I hope, by the aid of a recording aneroid already 
there, and a recording anemometer to be erected shortly, to be 
able to compare the changes of wind and pressure with the 
changes in the lake ; but I do not expect to find everything. 
Changes of level, &c., are going on in the earth surface, 
which, from an astronomical point of view, are intensely 
interesting, because they affect the instruments, and there- 
fore the measures. They are very minute, and we have no 
means of keeping a continuous record of them; but it is 
possible that if such changes affect the lake they will be so mag- 
nified by its comparatively enormous extent as to show them- 
selves on the recording instruments there. The baragraph at 
Sydney has shown long since that thunderstorms come on with 
a sudden rise of the barometer, which at times amounts to a 
tenth of an inch. If such a change could affect one end of the 
lake for a few minutes it would be equivalent to putting suddenly 
on to it aninch of water, which would make itself known at 
once bya rush to the other end; but although such changes 
must have some effect, I do not think it can be considerable, 
because, as I have elsewhere shown, these storms move at the 
rate of about 60 miles per hour, and are often 70 miles wide, so 
that such a storm coming on to the lake would spread all over it 
too rapidly to cause much motion in the water. I am here 
assuming that the storms there are of the same character as those 
which pass over Sydney, but they may be smaller when passing 
the lake, and travel more slowly. Certainly the storm which I 
saw coming down the lake did not traval with anything like such 
velocity. M. Waucher, who studied for years the motions of the 
same kind which take place in the Lake of Geneva, considered 
himself justified in saying: ‘‘ The lake is disturbed when the 
barometer is unsteady, and because of the varying pressure.” 
From what I have seen so far, the first part of this is true of 
Lake George, but it is not because the barometer is unsteady, 
but because at such times the wind is puffy and variable, and 
imparts to the water its own peculiarity. Of the power of the 
wind to set the water in motion I have mentioned several 
instances to-night, which I need not repeat, but I may add that 
the large impulses come from the north, because, as it seems to 
me, the wind from that direction acting on the water, the whole 
length of the lake has greater power than when blowing from 
the south over a short stretch of water, the gauge is fixed about 
a mile from the south end. But, although the wind is such an 
obvious cause of the phenomena under discussion, I think the 
barometric changes have some share in it, and there are some 
changes recorded which, so far, I am unable to refer to any 
cause. Mr. Russell then entered into details of the surroundings 
of Lake George, which, he stated, are of very great interest, 
viewed in the light of discussions as to the possible change in 
the amount of rainfall in the colony during long periods. The 
persistence of level in Lake George, he pointed out, is very 
strong evidence in favour of the view that there has been 
no great change in the rainfall there for thousands of years, 
and probably the same may be said of Australia. The rain- 
fall on the lake in 1870, Mr. Russell said, was 50 inches, 
double the average rainfall, which is 25 inches, and it is not to 
be wondered at that the lake rose at an unusual rate. Still this 
rain, heavy as it was, only served to cut little gutters in the older 
deposits which had been brought down the gullies. The primary 
object in placing the recording gauge on Lake George was to 
ascertain the rate of evaporation from such a large body of 
water, the conditions at the lake being very favourable for such 
an investigation. The record began on February 18, and the 
time since is too short to justify any assumption of the rate of 
evaporation there ; but I may mention some of the facts that 
have been recorded bearing upon this question. In 68 days the 
level of the lake has fallen 7 inches by evaporation ; in this in- 
terval, according to the records of rain-gauges at each end of 
the lake, 3°55 inches of rain has fallen, so that, ignoring the 
water which may have run from the hills during these rains, the 
lake has lost all the rain falling into it and 7 inches more, that 
is, 10f inches. During the past 14 years the lake has lost by 
evaporation 12 feet; and in May, 1878, the railway survey 
carried down the western side showed that the lake was then 
