282 Wisconsin Academy of Sciences, Arts and Letters. 
maintains nearly or quite parallel currents throughout the 
flowing stream. If this is correct then the thickness of the 
fli’m under restraint by the walls should be expected to be equal 
to about the radius of the capillary tube or, for water, about 
.025 millimeter. We have therefore presented three lines of 
evidence which appear to indicate a sphere of influence not less 
than .008 millimeter and perhaps not greater than .1 milli¬ 
meter or an average of say .05 millimeter for water. 
Suspension of Solids in Fluids. 
In taking up the study of soil solutions and the composition 
and amount of salt carried in them, one of the greatest obstacles 
encountered was the difficulty in obtaining a solution free from 
turbidity. Many of the soil particles are so minute as to 
readily pass the closest textured filter-paper in multiple layers 
after repeated filtration. Ho length of standing would render 
them clear and it was not permissible to clear them by the use 
of flocculating agents. The use of clay filters, of the Pasteur- 
Chamberlin type, was our final resort and proved to be thor¬ 
oughly effective and so effective, indeed, as I shall explain 
directly, as to retain entirely outside the filter walls such sol¬ 
uble salts as potassium nitrate, as shown by the fact that the 
last portions of a solution being passed through the filter ac¬ 
quired a greater concentration than the original. 
There are no soils which do not contain grains smaller in 
diameter than .001 millimeter, and not a small per cent of the 
finest soils consist of grains which are almost beyond the limits 
of the strongest microscope to resolve, which means that their 
diameters are close to, and probably even below .0003 millime¬ 
ters. But notwithstanding this extreme division it is an as¬ 
tonishing fact that, being times heavier than water, some 
of these particles will remain suspended indefinitely in a room 
approaching absolute quiet and where the diurnal range of tem¬ 
perature is less than a degree C., as we found to be the case in 
the subcellar constant-temperature room of the agricultural 
laboratory of the University of Wisconsin. 
