erroneous, and that this can be readily seen by inspection of a diagram
in which such balls are represented as forming a pile similar to the
well-known "pile of shells" of the algebras, in the diagram of which a
pile of three shells, resting on the base, has been omitted. It is then
seen that unless the pressures at an angle of 60° with the horizontal
are sufficient to produce frictional resistance of a very large amount,
the balls will roll and instantly break the arch action suggested by the
author. Consequently, an almost infinitesimal settlement of the
"centering" may cause the complete destruction of an arch of earth.

The author's logic is believed to be entirely faulty in many cases
because he repeatedly makes assumptions which are not in accordance with
demonstrated fact, and finally sums up the results by the statement: "It
is conceded" (line 2, p. 357, for example), when the writer, for one,
has not even conceded the accuracy of the assumptions. For instance, the
author's well-known theory that pressures against retaining walls are a
maximum at the top and decrease to zero at the bottom, is in absolute
contradiction to the results of experiments conducted on a large scale
by the writer on the new reinforced concrete retaining wall near the St.
George Ferry, on Staten Island, New York City, which will soon be
published, and in which the usual law of increase of lateral pressure
with depth is believed to be demonstrated beyond question. It must be
conceded that a considerable arch action (so-called) actually exists in
many cases; but it should be equally conceded by the advocates of the
existence of such action that changes in humidity, due to moving water,
vibration, and appreciable viscosity, etc., will invariably destroy this
action in time. In consequence, the author's reasoning in regard to the
pressures against the faces of retaining walls is believed to be open to
grave question as to accuracy of assumption, method, and conclusion.