ON A COMPKESSED-AIK FLYING-MACHINE. 57 



gum is dry, if a light. spray of water is blown over the paper a few 

 minutes suffices to make it as tight as a drum. 



It might be said that this flying-machine is not on the principle 

 enunciated by Borelli, because the wings are not continuous from 

 the tip to the body. But this is only a device to enable the wing 

 tips to act on the required quantity of air with less spread ; it 

 may possibly be one of those variations that make all the difference 

 between success and failure. These wings are also distinctly 

 double acting, and it is not quite clear that bird's wings thrust 

 during the up stroke ; but, as previously stated the question as to 

 the exact movement of a bird's wing is merely straw-splitting 

 when we have a mechanism that actually flies and is manifestly 

 imperfect in mechanical detail. 



In the transactions of the Institution of Naval Architects, Vol- 

 xxx., 1889, there is a paper by Beauchamp Tower, " On an 

 apparatus for providing a steady platform for guns &c. at sea." 

 The wheel revolving on a cup-bearing by tangential jets, and the 

 vertical axial jet nozzle playing on to the passages to the rams 

 (Tower has four rams, three would be better) is the germ of an 

 automatic apparatus for steering flying-machines level. 



As an instance of the unreliable nature of thrust diagrams taken 

 from the stationary machine, it may be mentioned that another 

 screw-driven one has been tried, Plate III. is the engine of it. 

 When the blades are set at 20° pitch angle a high thrust is got 

 on the indicator, but the machine flies a very short distance ; 

 when the blades are set at 45° a low thrust is shown by the 

 indicator card, but the machine flies 50% further. Coupling this 

 with the result obtained with the vibrating wings, it is reasonable 

 to suppose that screw machines should have the blades set parallel 

 to the screw- shaft, and allow the pitch to be automatically adjusted 

 by torsion. The blade surfaces of course being altogether abaft 

 the screw arms. This is a matter for the consideration of those 

 who prefer the screw to the flapping wings. 



Some may ask what is the use of experimenting in calm air when 

 such a state of the atmosphere is exceptional. But the answer is 

 that by patiently waiting for still air reliable data can alone be 

 obtained ■ and when we have the correct proportions of the 

 machines none of the parts can be more strained by a gale of wind 

 than by the lightest zephyr. The speed through the air does not 

 vary, it is only the distance over the ground that is affected. 



It has long been thought that there would be a spice of dange r 

 in trying large flying-machines, but now it is known that i 

 experiments are conducted over water a ducking is the only risk 

 involved, besides which the machine would be very slightly 

 damaged. 



