Reviews—Level of Ground-water, Wisconsin. 569 
as is observed in other places, is to stand highest under the highest 
ground, but to this there are several notable exceptions. When a 
prolonged dry period is followed by heavy rains, the water-surface 
under the low lands not infrequently stands above that under the 
higher areas. This is due partly to the low lands having less 
storage capacity on account of their smaller depth of soil, partly to 
the rains remaining for too short a time on the high lands to 
penetrate the soil, The measured height of water in a well is not 
always, however, a true index of the level of the neighbouring 
ground-water. It may be below the latter if the well be in 
constant use; and above it occasionally after protracted heavy 
rains, when the soil-air is unable to escape readily upwards through 
the supersaturated surface, but can be forced out of the wells, thus 
allowing the water to follow it. 
The rate at which the ground-water rises and falls varies 
between rather wide limits, but, as a rule, a given rise occupies 
a much shorter time than the same fall. The water generally 
falls more rapidly in the shallow than in the deep wells, partly 
on account of the shorter distance to the drainage outlet making 
the resistance to the flow less, partly from a more rapid loss of 
water at the surface of the ground through combined capillary 
and root action, After a fall of rain the rise of the ground- 
water takes place almost immediately in the shallow wells, but 
lags behind for two or three days in the deep ones, the average 
rise being 0:42 foot, or about five inches, for a rainfall of one 
inch. The rate at which the water-level falls is much greater 
when the barometer is rising than when it is falling; during the 
three years 1888-90 the mean daily fall was 0224 inch with a 
rising, and 0-001 inch with a falling, barometer. Again, the water- 
level falls more rapidly during the day than during the night, the 
average fall for a number of wells being 8-583 inches per 1000 day- 
hours (6 a.m. to 6 p.m.) and 1:309 inches per 1000 night-hours 
(6 p.m. to 6 a.m.). 
The general surface of the ground-water is also subject to 
numerous oscillations of small extent, some of which are almost 
microscopic in amplitude, so that it is rare for it to be ever quite 
at rest. ‘<The equilibrium of the water in the capillary soil-spaces 
above the surface of the ground-water is so unstable that apparently 
the slightest cause is sufficient to upset it, causing the water to flow 
out into the non-capillary spaces, but only to be returned again, 
often on a moment’s notice. .... The geologic and agricultural 
significance of these movements must be very great, for here is a 
water-washed zone of rock and soil, having the combined area of all 
land above the ocean level, unless we must except those of the polar 
zones, which is alternately flooded with water and then exposed to 
air; and this zone, rising and falling through greater and lesser 
distances, according to the secular and short period changes in the 
level of the ground-water, must greatly exaggerate the solvent 
power of soil-water over what it would be did these oscillations not 
exist” (p. 44). 
