RESEARCH METHODS IN STUDY OF FOREST ENVIRONMENT. 75 
for^the well soil, can never be considered as an exact measure of the 
moisture outside. The well samples will be principally useful in 
showing changes, and without doubt should occasionally be compared 
with native samples taken near by. It is believed, however, that for 
practical purposes a certain constant relation between the two soils 
may be assumed. So far, because of the great difficulty of actual 
contact tests between two soils, the moisture ratio at equilibrium 
must be established on theoretical considerations. 
From what is known of capillary movement in soils (116) it would 
seem that, when the moisture content of two soils is near the satura- 
tion point, they will be in equilibrium at moisture values measurable 
by the amount which either soil can hold against the force of gravity. 
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Similarly, at much lower moisture contents, the amounts which 
the two soils hold against a force one hundred or one thousand times 
as great as gravity, woLild appear to establish a basis for equilibrium. 
But, in view of the fact that at a low-moisture content actual capil- 
lary movement becomes negligible while transfer from one to the 
other by the vapor-transfer method can be readily accomplished, it 
seems more logical that we should consider an equilibrium existing 
which would mean equal osmotic pressures- in the two soils. These 
points can be determined for each soil by freezing-point depressions 
or by assuming equal osmotic pressures at the wilting coefficients. 
Diagram 3 shows a method for working out a scale of relations for 
the soil of any well and soil from three depths, obtained when the 
well was dug. The curve for the well soil is a straight line whose 
