VII FLIGHT 273 
that the propelling force must act by means of wings. 
Quite recently Herr Lilienthal has tried to navigate 
the air with an equipment resembling a bird’s. But 
though his wings have enabled him, starting from 
an elevation, to sail over 800 yards before sinking to 
earth—a truly wonderful feat of pluck and skill— 
it is improbable that any one could ever succeed 
by the help of such appliances in rising and main- 
taining himself in the air; and nothing short of this 
can be called flight. Mr. Maxim has advanced a great 
deal further. He has seen that we ought not, in 
trying to rival a bird, to imitate it slavishly, as the 
first sewing-machine is said to have imitated the 
hand-sewn stitch, and he has, therefore, employed 
screws for the propulsion of his flying-machine. In 
animal mechanism, where the different parts cannot 
be separated, screws are, of course, out of the question. 
In man-made machinery a screw is better than a lever. 
It has no idle intervals, whereas a wing during the 
upstroke would be no better than a parachute. 
Besides this, it is doubtful whether machinery would 
not be too clumsy to effect all the turns that a wing 
must make even in straight-ahead flight. As soon as 
Mr. Maxim’s machine was allowed to run along its 
line of rails at a rate of thirty-six miles per hour, it 
rose in the air, and but for contrivances designed to 
restrain it from mounting more than a very little, there 
is no knowing what heights it might have reached. 
This great aeroplane, weighing 8,000 lbs., imitates a 
sea-bird rising from the water: it presents to the air 
a surface inclined slightly upward, and this inclined 
surface causes it to rise when it travels fast. But 
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