y, on
Staten Island."

The writer's "well-known theory that pressures against retaining walls
are a maximum at the top and decrease to zero at the bottom" applies
only to pressures exerted by absolutely dry and normally dry material,
and it seems to him that this so-called theory is capable of such easy
demonstration, by the simple observation of any bracing in a deep trench
in material of this class, that it ought to be accepted as at least
safer than the old theory which it reverses. As to this "well-known
theory" in material subject to water pressure, a careful reading of the
paper, or an examination of Fig. 12 and its accompanying text, or an
examination of Table 1, will convince Mr. Goodrich that, under the
writer's analysis, this pressure does not decrease to zero at the
bottom, but that in soft materials it may be approximately constant all
the way down, while, in exceptionally soft material, conditions may
arise where it may increase toward the bottom. The determination should
be made by taking the solid material and drying it sufficiently so that
water does not flow or seep from it. When this material is then
compacted to the condition in which it would be in its natural state,
its angle of repose may be measured, and may be found to be as high as
60 degrees. The very fine matter should then be separated from the
coarser material, and the latter weighed, to determine its proportion.
Subtracting this from the total, the remainder could be credited to
"aqueous matter." It is thus seen that with a material when partially
dried in which the natural angle of repose might be 60 deg., and in which
the percentage of water or aqueous matter when submerged might be 60%,
there would be an increase of pressure toward the bottom.

The writer does not know the exact nature of the experiments made at St.
George's Ferry by Mr. Goodrich, but he supposes they were measurements
of pressures on pistons through holes in the sheeting. He desires to
state again that he cannot regard such experiments as conclusive, and
believes that they are of comparative value only, as such experiments do
not measure in any large degree the pressure of the solid material but
only all or a portion of the so-called aqueous matter, that is, the
liquid and very fine material which flows with it. Thus it is well known
that, during the construction of the recent Hudson and North River
Tunnels, pressures were tested in the silt, some of which showed