FIRST PRINCIPLES OF AERIAL TRANSIT. 
365 
and the force expended nearly equal to half a horse power. We 
thus see that not by any practicable extension of surface is it 
possible for man to raise himself perpendicularly in air by his 
own muscular force, the data haying been taken under the most 
favourable estimate, without deducting for loss arising from the 
friction of a motive machine. 
This may be conformable to the opinion of the large class of 
antivolants, and is consistent with the assertion of some who 
are professed scientists ; but the argument does not end here, 
for the conditions named do not truly represent any form of 
flight, which strictly means one of horizontal progress. Many 
of the gallinaceous birds located in forest tracts, by aid of wings 
of the largest area and a great temporary exertion of strength, 
are able to raise themselves nearly perpendicularly into the 
branches above, but they are so incapable of taking long flight 
that when pursued in an open country they prefer running to 
flying as a means of escape. 
Numerous experiments have been made by man to raise him- 
self by various machines perpendicularly in air, but they have 
all failed ; and this about represents the summary of all that 
has yet been done in the science of aeronautics by mechanical 
means only. 
Another effect remains to be considered. Instead of allowing 
the weighted plane to fall perpendicularly, let it be moved 
rapidly in a horizontal direction while still free to descend. The 
rate of descent under these circumstances would be immensely 
retarded, according to the speed given. A fresh, unmoved 
stratum of air quickly acted upon every instant with its inertia 
undisturbed offers great resistance to deflection, and from this 
cause, at a very high speed, affords a nearly solid support. 
This condition serves to explain the mystery, and involves the 
true principle of flight, which depends not upon large area, but 
on the width of the stratum, and consequently the weight of air 
passed over in a brief time. All the data for exact calculations 
are yet wanting. If the air were non-compressible, like water, 
an accurate result could be foretold of the lifting force of in- 
clined surfaces ; but air being elastic, a formula is required 
differing from that applic- 
^ a able to a dead weight, and 
therefore the theory can only 
be put forth in demonstra- 
tive forms. Let a be a 
plane surface in the form of 
a square , and while con- 
strained to a horizontal posi- 
tion during descent, let a weight or ball (b) be set at one ex- 
tremity. The fall through air in a given period to be from a to c. 
d 
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