scale in order to measure accurately the pressures due to sands and
earths of varying characteristics, it appears to be conclusive in
showing the principle, and near enough to the theoretical value to be
taken for practical purposes in designing structures against water
pressures when buried in sand or earth.

It should be carefully noted that the friction of the water through
sand, which is always a large factor in subaqueous construction, is
virtually eliminated here, as the water pressure has to be transmitted
only some 6 or 8 in. to actuate the base of the piston, whereas in a
tunnel only half submerged this distance might be as many feet, and
would be a considerable factor.

It should be noted also that although the area subject to pressure is
diminished, the pressure on the area remaining corresponds to the full
hydrostatic head, as would be shown by the pressure on an air gauge
required to hold back the water, except, of course, as it may be
diminished more or less by friction.

The writer understands that experiments of a similar nature and with
similar apparatus have been tried on clays and peats with results
considerably higher; that is, in one case, there was a pressure of 40
lb. before the piston started to move.

The following is given, in part, as an analysis and explanation of the
above experiments and notes:

It is well known that if lead be placed in a hydraulic press and
subjected to a sufficient pressure it will exhibit properties somewhat
similar to soft clay or quicksand under pressure. It will flow out of an