measured, and the bottom of the larger bucket was covered over with sand
so that in setting solidly in the sand the inside bucket would occupy
the same relative position as it did in the water. The same weight was
then applied and would not begin to lift the inner bucket. For instance,
in the first part of the experiment the weight stood at 12 in. from the
pivot, while in the next step the weight, standing at the end of the
bar, had no effect, and considerable external pressure had to be exerted
before the bucket could be lifted. Immediately after it was relieved,
however, the weight at 12 in. would hold it clear of the sand. No
attempt was made to work the bucket into the sand; the sand was leveled
up and the bucket was seated on it, turned once or twice to insure
contact, and then allowed to stand for some time before making the
experiment. No attempt was made to establish the relationship between
sands of varying voids, the general fact only being established, by a
sufficient number of experiments, that the weight required to lift the
bucket was more than double in sand having 40% of voids than that
required to lift the bucket in water only.

[Illustration: FIG. 9.]

_Experiment No. 6._--The apparatus for this experiment consisted
essentially of a hydraulic chamber about 8 in. in diameter and 1 ft.
high, the top being removable and containing a collar with suitable
packing, through which a 2½-in. piston moved freely up and down, the
whole being similar to the cylinder and piston of a large hydraulic
jack, as shown in Fig. 1, Plate XXVIII. Just below the collar and above
the chamber there was a ½-in. inlet leading to a copper pipe and thence
to a high-pressure pump. Attached to this there was a gauge to show the
pressure obtained in the chamber, all as shown in Fig. 9. The purpose of
the apparatus was to test the difference in pressure on any object