more polite than "guess").

The author has stated, however, that when the tunnel roof and sides are
in place, no further trouble need be feared. On the contrary, in 1885,
the Canadian Pacific Railroad built a tunnel through clayey material and
lined it with ordinary 12 by 12-in. timber framing, about 2 or 3 ft.
apart. After the tunnel was completed, it collapsed. It was re-excavated
and lined with 12 by 12-in. timbers side by side, and it collapsed
again; then the tunnel was abandoned, and, for some 20 years, the track,
carried around on a 23 deg. curve, was used until a new tunnel was built
farther in. This trouble could have been caused either by the sliding or
swelling of the material, and the speaker is inclined to believe that it
was caused by swelling, for it is known, of course, that most material
has been deposited by Nature under great pressure, and, by excavating in
certain materials, the air and moisture would cause those materials to
swell and become an irresistible force.

To carry the load, Mr. Meem prefers to rely on the points of the piles
rather than the side friction. In such cases the pile would act as a
post, and would probably fail when ordinarily loaded, unless firmly
supported at the sides. The speaker has seen piles driven from 80 to 90
ft. in 10 min., which offered almost no resistance, and yet, a few days
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