In 1872 some experiments were made for the Aeronautical Society on the
pressure of air on oblique planes. These plates, of 1 to 2 ft. square,
were balanced by ingenious mechanism designed by F. H. Wenham and
Spencer Browning, in such a manner that both the pressure in the
direction of the air current and the lateral force were separately
measured. These planes were placed opposite a blast from a fan issuing
from a wooden pipe 18 in. square. The pressure of the blast varied
from 6/10 to 1 in. of water pressure. The following are the results
given in pounds per square foot of the plane, and a comparison of the
experimental results with the pressures given by Duchemin's rule.
These last values are obtained by taking P = 3.31, the observed
pressure on a normal surface:--
+-----------------------------------+-------+-------+-------+------+
| Angle between Plane and Direction | 15° | 20° | 60° | 90° |
| of Blast | | | | |
+-----------------------------------+-------+-------+-------+------+
| Horizontal pressure R | 0.4 | 0.61 | 2.73 | 3.31 |
| Lateral pressure L | 1.6 | 1.96 | 1.26 | .. |
| Normal pressure [root](L² + R²) | 1.65 | 2.05 | 3.01 | 3.31 |
| Normal pressure by Duchemin's rule| 1.605 | 2.027 | 3.276 | 3.31 |
+-----------------------------------+-------+-------+-------+------+