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 ¾-in. projection on two sides, and a false bottom was placed below
and outside of the original bottom, with bolts running through it,
keying to washers on top of the sand, with which the box was partly
filled. One side of the box contained a glass front, in order that
conditions of saturation could be observed. The box of sand was then
filled with water and, after saturation had been completed and the nuts