Hydrology. — “On the Motion of Ground Water in Frost and 
Thawing Weather.’ By Prof. Bue. Dugoss. 
(Communicated at the meeting of January 29, 1921). 
From small pools, from detached ditches, especially with high 
sides, from wheel tracks, water is seen to disappear on prolonged 
frost from under the ice formed, so that beneath the ice there are 
air-filled spaces. The vanished water-layer can be from a few centi- 
meters to some decimeters thick. The phenomenon is universally 
known, but the question what happens to the water, has not been 
answered as yet. 
Other, equally common phenomena, are observed in thawing 
weather. Before the frost the soil may have been fairly dry near 
the surface, but without previous snow or rain it is found to be 
muddy on the still frozen substratum, as soon as thaw has set in. 
Not until the frost has quite gone from the ground, the superficial 
soil resumes its former, less wet condition, because then the excess 
of water sinks away. Whence this excess of water? 
When the frost has gone from the ground, new-set plants that 
had not yet properly taken root, may be found “frozen up’, that 
is partly, in some cases of small plants entirely, uprooted. By 
what cause? 
Some winters, especially that of 1917/18, I had an opportunity to 
make observations in the ‘‘sand-diluvium” of central Limburg, which, 
I think, can throw some light on the causes of these phenomena. 
The most important fact found, was that i thawing weather the 
ground water rises. Without snow or rain, and without superficial 
inflow of water, the level of the water, among others in ditches, after 
the ice in them had melted, is seen to rise in the district mentioned 
to such an amount as 1 em. per twenty-four hours. 
Hence there is displacement of ground water, during frost upwards, 
and during thaw downwards, and I imagine this to take place as 
follows. 
The pressing action of the surface tension of the water that sur- 
rounds the ground grains, decreases with increasing diameter. Hence 
in the state of equilibrium the coarse ground grains are covered 
with thicker water layers than the fine ground grains. And just as 
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Proceedings Royal Acad. Amsterdam. Vol. XXIII. 
