later, they would sustain 40 tons each. No one would dream of putting 40
tons on a 90-ft. pile resting on rock, if it were not adequately
supported.

It is the speaker's opinion that bracing should not be omitted for
either piles or coffer-dams.


CHARLES E. GREGORY, ASSOC. M. AM. SOC. C. E.--In describing his
last experiment with the hydraulic chambers and plunger, Mr. Meem states
that, after letting the pressure stand at 25 lb., etc., the piston came
up. This suggests that the piston might have been raised at a much lower
pressure, if it had been allowed to stand long enough.

The depth and coarseness of the sand were not varied to ascertain
whether any relation exists between them and the pressure required to
lift the piston. If the pressure varied with the depth of sand, it would
indicate that the reduction was due to the resistance of the water when
finely divided by the sand; if it varied with the coarseness of the
sand, as it undoubtedly would, especially if the sand grains were
increased to spheres 1 in. in diameter, it would show that it was
independent of the voids in the sand, but dependent on dividing the
water into thin films.

The speaker believes that the greater part of the reduction of pressure
on the bottom of the piston might be better explained by the viscosity
of the water, than to assume that a considerable part of the plunger is
not in contact with it. The water, being divided by fine sand into very
thin films, has a tensile strength which is capable of resisting the
pressure for at least a limited time.