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POPULAR SCIENCE REVIEW. 
But during the descent let the hall have a horizontal course at 
the top of the plane from b to d ; of course, in this case, the rate 
of descent will not he altered whether the hall is stationary or 
in motion — it is simply a question of area and relative weight. 
But suppose the velocity of the hall is doubled, so as to carry it 
over a space equal to the end of a second similar plane, the hall 
will then descend only half the distance in the same time. If 
the velocity is trebled, so as to carry it on as far as the end of 
plane No. 3, the ball will fall only one-third the distance ; and 
so on with a reduction of fall proportionate to the rate of 
traverse. This is illustrative of the influence of a high hori- 
zontal speed on the rate of fall, hut it may also he demonstrated 
how this rate of fall at the same speed may be greatly reduced 
hy the form and disposition of the surface, relative to the di- 
rection of motion. 
The foregoing surface is assumed as a square , hut suppose 
this to he cut in half and the two lengths added end to end 
transversely to the line of motion, the area remains just the 
same as before, and the fall will still be from a to c, while the 
ball passes only half the distance ; but let the ball travel at the 
same speed as on the first plane, it will then pass over another 
similar elongated element of only half the width, and take 
double the time to descend to c ; or, in other words, by this 
disposition of area the supporting power of the surface will be 
increased nearly two-fold. 
Again, if cut into four and extended the same way, its value 
will be quadrupled. 
Having as yet no flying contrivance of our own construction 
that can be independently propelled through free air at a high 
speed in order to exemplify this theory, we must refer to the 
formation and action of a bird’s wing for a working example. 
The most remarkable one is the wandering albatross. This 
■ extraordinary bird is found thousands of miles away from land, 
and may be said to live in the air, for in stormy weather it 
never rests on the ocean, but gathers up the floating substances 
that serve it for food during flight. The wings extend fifteen 
feet from end to end, and are only eight and a half inches in 
width at the broadest part. The bearing afforded by such a 
wide stratum of air may be considered as almost an unyielding 
one at the usual rate of speed, and in consequence it is able to 
swoop down, and rise again apparently to the same height, by 
the mere momentum of its own body, with no aid by the im- 
pulses of the wing. The bird could not perform this feat if its 
aerial support was a rapidly yielding one, but would require to 
flap diligently in order to regain its former level. 
The albatross also affords the best visible indication of the 
power consumed for maintaining its flight. Many observers 
