44 NOTES ON FLYING-MACHINES. 
strike the wall. I purpose selecting the best of these models, inal 
making their mean dimensions a standard from which to take a 
fresh departur 
Each wing ties been made to have a stroke of 90°, but in short 
wings this may be largely increased with advantage, as we see 
several kinds of pigeons even striking their wings together ; long- 
winged, swift-flying birds use an angle much less than 90°. 
At first I stretched the india-rubber from aft forward, but in 
upwards at starting, we want the centre of gravity moved forwa 
to decrease the angle of elevation as the power of the elastic 
decreases. 
Another note-worthy point is, that the fore-and-aft members of 
the planes are placed underneath the web, and the tranverse ones 
above it. 
The distance these models fly seems very trifling, but experience 
teaches us that in all model-experiments increase > of proportional 
size and weight bring universally better results in work done, 
It has been found impossible to form even a moderately exact 
determination of what distance or height the machines actually 
fly ; the pe tena of the air in a room like this causes currents 
that tilt the wings or tail so that the action is different at each 
trial.* Out of doors accuracy is still more impossible until we aad 
the machines much larger, and consequently less fragile. A wi 
torn and patched again of course renders all previous trials vattee: 
less for comparison: and besides all this, whatever care is taken 
not to project the machine in the direction it is wished to go, there 
is still probably an involuntary movement of the hand in that 
irection which you will perhaps detect. 
The speed attained shows us that when we come to deal with 
machines weighing tons instead of ounces we shall have also to deal 
with air-pressures exceeding hurricane force, with which the edges 
of trochoided planes are in my opinion the only things that can 
successfully cope. 
The steering of flyi ing-machines on this principle requires a 
rapidity of aes and action that will at first tax the nerves to 
the ost, but in one-man machines practice will reduce the 
movements of the body necessary to alter the centre of gravity to 
the various requirements to as simple an act of volition as skating 
* Nore 7, Ate, 
upwards on on reaching th stars it: Repro cer not Seas ar Gain 
__ is now seen to to have been that the main ee sie want citealating 
