56 LOCAL VARIATIONS AND VIBRATIONS OF EARTH'S SURFACE. 
and the lake gauge for these reasons is not only capable of showing 
changes quite as minute as the Cambridge pendulum apparatus, 
but also of keeping a perfectly satisfactory record of these changes, 
so written that many, if not all, the causes can be traced in the 
curves se they produce. 
months since I had not looked for any diurnal effect, and 
Fre did not see it, although it was clearly marked in almost 
very sheet that had been taken off up to that time. These curves 
are small, but there can be no question as to their existence; they 
are shown as clearly as the larger — although, of course, ona 
small scale. In Europe the pendulum was seen to swing north- 
wards, or away from the equator during + the day and towards it at 
ht ; and so the water of Lake George runs away from the 
equator during the day and towards it at night, and this curve can 
be traced as something added on to all others, (see photoliths of 
sheets attached), except of course when a strong wind takes entire 
control of the lake. The diurnal change of level seldom exceeds 
half an inch, but a tenth of an inch can easily be seen, and this 
corresponds toa change in the vertical at the lake of 0: 016", an 
angle so small that even lunar effects may produce double that 
M d’Abbadie, namely, 2:4”, it would mean a change of 15 inches, 
or toes times as much as can be easily seen in the records at Lake 
Geo 
The. reference here is to slow changes extending over five or s 
hours or days, and no such change in the level “of mn lake hai 
appeared during the four months the gauge has been at wor. 
Nor can I hear that any such changes of level rat ever been 
seen by those who have resided at the lake for ll 
changes of this kind do occur at long intervals, but they are so 
small that it would seem the earth’s surface at the lake is more 
rigid than it is in Europe; or that some of the observations 
ni ae there do not — changes in the earth’s surface, but 
in the instruments used. of these small changes i - shown in 
the photolith of the sheet Jae 27 to August 3. On July 27th 
_ the water in the lake was rough, owing to a northerly wind. 
About 8 a.m. of 28th the north wind ceased, and the weather 
became remarkably calm; yet the water fell 6} inches in two 
hours, and a series of periodic waves, much larger than those 
caused by the wind, was set up, and the mean level of the water 
during all day of 28th was 14 inch lower than during the 27th. 
‘This weer i in level might be accounted for by the falling of the 
north wind the water recovering its normal peenene but for 
the fact that at 9 am. on July 29th the water sudd rose 
_. again while the weather was quite calm. I have not drawn 
_ mean line through these waves; its position is so obvious that 
