The inside bucket was then given a false
bottom and partly filled with wet sand, resting on the sand in the
larger bucket. Both were filled with water, and the weight, _W_, Fig. 7,
on the arm was shifted until it balanced the weight of the inside bucket
in the water, the distance of the weight, _W_, from the pivot being
noted. The false bottom was then removed and the inside bucket, resting
on the sand in the larger one, was partly filled with sand and both were
filled with water, the conditions at the point of weighing being exactly
the same, except that the false bottom was removed, leaving the sand in
contact through the 6 by 6-in. opening. It is readily seen that, if the
sand had possessed the aqueous properties sometimes attributed to sand
under water, that in the inside bucket would have flowed out through the
square hole in the bottom, allowing it to be lifted by any weight in
excess of the actual weight of the bucket, less its buoyancy, as would
be the case if it contained only water instead of sand and water. It was
found, however, that the weight, resting at a distance of more than
nine-tenths of the original distance from the pivot, would not raise the
inside bucket. On lifting this inside bucket bodily, however, the water
at once forced the sand out through the bottom, leaving a hole almost
exactly the shape and size of the bottom orifice, as shown in Fig. 1,
Plate XXVII. It should be stated that, in each case, the sand was put in
in small handfuls and thoroughly mixed with water, but not packed, and
allowed to stand for some time before the experiments were tried, to
insure the compactness of ordinary conditions. It is seen from Fig. 1,
Plate XXVII, that the sand was stable enough to allow the bucket to be
put on its side for the moment of being photographed, although it had
been pulled out of the water a little less than 3 min.

[Illustration: PLATE XXVI, FIG. 1.--TYPES OF ARCH TIMBERS USED IN
BAY RIDGE TUNNEL SEWER.]

[Illustration: PLATE XXVI, FIG. 2.--NORMAL SLOPE OF LOOSE SAND,
GRAVEL, AND CEMENTED GRAVEL, IN CLOSE PROXIMITY.]

_Experiment No. 3._--In order to show that the arching properties of
sand are not destroyed under subaqueous conditions, a small sand-box,
having a capacity of about 1 cu. ft., and similar to that described in
Experiment No. 1, was made. The bottom was cut out, with the exception
of a 3/4-in. projection on two sides, and a false bottom was placed below
and outside of the orig