oIj aerial navigation. Jg^ 



tlie moving power will be left at full liberty to produce the 

 waft necessary to bend up the hinder edge of the wing, and 

 gain tlie propelling power. A bow is not in fact an equable 

 spring, but may l)e made so by using a spiral fusee. I have 

 made use of it in this place merely as the most simple mode 

 of stating the principle I wished to exhibit. Should aorcylindttr 

 counterbalancing spring of this kind be adopted in the ^."'^ ^ '^•*S 

 practice of aerial navigation, a small well polished cylinder, 

 furnished with what may be termed a bag piston (upon the 

 principle made use of by nature in preventing the return of 

 the blood to the heart, when it has been driven into the 

 aorta, by the intervention of the semilunar valves) would, by 

 a vacuum being excited each stroke of the wing, produce 

 the desired effect, with scarcely any loss by friction*. These Farther uses of 

 elastic agents may likewise be useful in gradually stopping these. 

 the momentum of large surfaces when used in any alter- 

 nate motion, and in thus restoring it during their return. 



Another principle, that may be applied to obviate this Another me- 



leverao^e of a wing, is that of usiny; such a construction as '^"'^ : "inking 



•^ =• . "^ . the air coun'- 



will make the supporting power of the air counterbalance terbaianc* 



itself. It has been before observed, that only about one ''^'^^^• 

 third of the wing in birds is applied in producing the pro- 

 pelling power; the remainder, not having velocity sufficient 

 for this purpose, is employed in g^iving support, both in the 

 beat and retvirn of the wing. 



Let A and B, fig. 2, be two wings continued beyond the 

 pole or hinge upon which they turn at C. If the extreme 

 parts at A and B be long and narrow, they may be balanced, 

 tvhen in the act of skimming, by a broad extension of less 

 length on their opposite sides ; this broad extension, like the 



* I have made use of several of these pistons, and have no scruple Excellence of 

 in asserting, that for all blowing engines, where friction ii an evil, and the bag piston, 

 being very nearly airtight is sufficient, there is no other piston at all 

 comparable with them. The most irregular cylinder, with a piston of 

 this kind, will *ct with surprising effect. To give an instance; a cy- 

 linder of sheet tin, 8 inches long and 3| in diameter, required 4 pounds 

 tn force the piston down in 15 minutes; and in other trials be- 

 came perfectly tight in same positions, and would proceed no' farther. 

 The fiiction, when the cylinder was open at both ends, did not exceed 

 \ an ounce. 



Idweir 



