* 
176 Transactions, —Miscellaneous. 
. oblique stroke. ~ As the anterior edge of the wing is only slightly elevated in 
flight, a considerable upward pressure is received during the down-stroke of 
the > wing as the air reacts on the concave side. As this stroke involves the 
most work, therefore the muscles which effect it are of great size and 
strength. We must not suppose that the up-stroke of the wing is only *3 
useful to so raise it as that it can be again depressed, for in the up-stroke 
' we may detect one of the main provisions for its onward transit ; ; for i in the S 3 
up-stroke, as the anterior portion of the wing is still more or less elevated, E 
it is clear that a powerful forward scat is thus given to the wing and — 
thence to the bird. 
a: it is much easier to move the wing upwards than downwards, asthe __ 
upper and convex side meets less resistance from the air, therefore the  — 
upward stroke is effected by smaller and weaker muscles, cone probably in 
a more disadvantageous position. 
From the form and structure of birds and from " eu observa- 
tions, it is apparent that a comparatively small force will start and propel 
them horizontally to that which is required to sustain them against the 
force of gravity ; : hence the attempt in the model before us to oe 
sails or wings that the tips are kept at a small but precise angle, and the 
whole length thereof is by its construction, when in action, compelled to 
assume à slight conca . Thereis, however, a limit to this concavity, for 3 
as the principal part of the weight of the wheel is at the circumference, 
therefore. ie greater the speed the greater is the centrifugal force of all parts 
of the cireumference, thus inereasing the tension; the very slight Mc 
of the rim thus coming into action. * El 
=. 
ma 
Art. XVI.—Introduction of the Principle of the Gyroscope in Aerial Transit. 
y Henry KEY +. ee 
pae 
Plate IV. 
[Read before the Otago Institute, 9th October, 1877.] 
— our ideas of stability of direction and position are but relative, and the 
same law which expresses that all matter moves in straight lines until 
deflected by another force, and which regulates a planet in its h, 
give stability to an aerial machine, so that it can be propelled and s 
in any direction even against moderate winds; indeed the most pert X 
thing in nature is the axis round which a ayota body rotates ; 
hue many familiar instances of the permanency of the plane of rotation, 
child's eee tops and-hoops, then again the wheels of ou 
