many of the conclusions drawn therefrom cannot be
accepted without further demonstration.

FRANCIS W. PERRY, ASSOC. M. AM. SOC. C. E.--Pressure-gauge
observations on a number of pneumatic caissons recently sunk, through
various grades of sand, to rock at depths of from 85 to 105 ft. below
ground-water, invariably showed working-chamber air-pressures equal, as
closely as could be observed, to the hydrostatic pressures computed, for
corresponding depths of cutting-edge, as given in Table 2.

These observations and computations were made by the speaker in
connection with the caisson foundations for the Municipal Building, New
York City.

TABLE 2.--EQUIVALENT FEET OF DEPTH BELOW WATER PER POUND
PRESSURE.

Pressure, |Equivalent |Equivalent |Observed |
in |feet of |elevation |pressure. |
pounds. |depth. |for water | |
| |at--6.85. | |
|___________|_____________| |
| | | |
|M.H.W. |Ground-water.| |
__________|___________|_____________|______________|
| | | |
1 | 2.31 | 9.06 |Practically |
2 | 4.63 | 11.48 |the same as |
3 | 6.94 | 13.79 |computed |
4 | 9.25 | 16.10 |for |
5 | 11.57 | 18.42 |ground-water. |
6 | 13.88 | 20.73 | |
7 | 16.19 | 23.04 | |
8 | 18.50 | 25.35 | |
9 | 20.82 | 27.67 | |
10 | 23.13 | 29.98 | |
11 | 25.44 | 32.29 | |
12 | 27.76 | 34.61 | |
13 | 30.07 | 36.92 | |
14 | 32.38 | 39.23 | |
15 | 34.70 | 41.55 | |
16 | 37.01 | 43.86 | |
17 | 39.32 | 46.17 | |
18 | 41.63 | 48.48 | |
19 | 43.95 | 50.80 | |
20 | 46.26 | 53.11 | |
21 | 48.57 | 55.42 | |
22 | 50.89 | 57.74 | |
23 | 53.20 | 60.05 | |
24 | 55.51 | 62.36 |