difference between
angles of repose produced in this manner by the rolling friction of
particles and the internal angles of friction, which must be used in all
earth-pressure investigations, has been repeatedly called to the
attention of engineers by the writer.[H]

The writer's experiments are entirely in accord with those of the author
in which the latter claims to demonstrate that "earth and water
pressures act independently of each other," and the writer is much
delighted that his own experiments have been thus confirmed.

In Experiment No. 3, the query is naturally suggested: "What would have
been the result if the nuts and washers had first been tightened and
water then added?" Although the writer has not tried the experiment, he
is rather inclined to the idea that the arch would have collapsed. With
regard to Experiment No. 5, there is to be noted an interesting
possibility of its application to the theoretical discussion of masonry
dams, in which films of water are assumed to exist beneath the structure
or in crevices or cracks of capillary dimensions. The writer has always
considered the assumptions made by many designing engineers as
unnecessarily conservative. In regard to the author's conclusions from
Experiment No. 6, it should be noted that no friction can exist between
particles of sand and surrounding water unless there is a tendency of
the latter to move; and that water in motion does not exert pressures
equal to those produced when in a static condition, the reduction being
proportional to the velocity of flow.

The author's conclusion (p. 371), that "pressure will cause the
quicksand to set up hydraulic action," does not seem to have been
demonstrated by his experiments, but to be only his theory. In this
instance, the results of the writer's experiments are contrary to the
author's theory and conclusion.

The writer will heartily add his protest to that of the author "against
considering semi-aqueous masses, such as soupy sands, soft concrete,
etc., as exerting hydrostatic pressure due to their weight in bulk,
instead of to the specific gravity of the basic liquid." Again,
similarly hearty concurrence is given to the author's statement:

"If the solid material in any liquid is agitated, so that it is
virtually in suspension, it cannot add to the pressure, and if
allowed to subside it acts as a solid, independently of the water
contained with it, although the water may change