172 Tr ansac tio ns.—Miscel laneous . 
These apparent paradoxes may be partly explained when we consider 
the perfect elasticity of the air; for when it strikes the point P it then, 
after compression, by virtue of its elasticity, diverges from P at all angles 
along the plane; so readily does it escape laterally that it appears to draw 
a large volume of formerly quiescent air down too. 
Experiment, No. 4.—Reversing experiment No. 8, “action and re- 
action being equal and contrary,” it follows that when a plane 4 P B 
(figure 2) oblique to the horizon is carried with its upward and anterior 
edge in a horizontal direction, the tendency of the incident current I P 
is not to be reflected along the line P Q, but the air is retained closer to 
the surface of the plane, which fact must very materially increase the 
lateral pressure, and therefore greatly assist in buoying up the plane. 
Experiment, No. 5.—In order to ascertain the lifting pressure exerted by 
the inertia and elasticity of the air on a plane set at various angles and 
travelling with a given velocity, the apparatus here exhibited was devised ; 
it consists of a thin sheet of metal a foot square, so connected with a spring 
balance that it can be set to any given angle. Action and reaction being 
equal and contrary, it is clear that if this instrument be set in a current of 
air the same effects are obtained as if the plane were moved at the same 
velocity through still air. The instrument was placed in a strong wind, 
and when the plane was first placed at a right angle to the current, with 
the spring so arranged as to show the horizontal pressure, it registered an 
average pressure of 2-7 lbs. on the square foot, indieating a velocity of the 
air of 23 miles per hour. The instrument was then so arranged as to 
measure the vertical pressure when the plane was set at various angles to - 
the horizon. "The following table gives a summary of the average results 
of a number of experiments therewith :— 
ANGLE TO HORIZON. LIFTING PRESSURE IN LBs. 
5? 1:13 
10° 1:43 
20? 1:65 
30° 1:83 
40° 2:00 
50° 1:80 
By this we see that the lifting pressure of a plane one foot square travelling 
through still air is more than half as great at an angle of 5° as it is at 40°, 
while we know that the resistance to its forward or horizontal motion is 
almost removed, for considerably less air has to be displaced. In fact, the 
inertia of the air is utilized with small angles, for considerably greater 
velocity can be imparted to the plane with the same expenditure of force. 
_ From the foregoing experiments it appears that the law of “resolution 
of forces ” as applied to solids is inapplicable in the case of gases. More- 
