ON AERIAL NATtGATiaN. ^ §3 



to restore the equilibrium in this case, as tended to dcistroy 

 it in the other: tlie operation very much reieujbling what 

 takes phice in the common boat*. 



This angular form,^ with the apex downward, is the chief B;isi3 of stabi- 

 basis of suil)iUtv in aerial navio'ntiou ; but as tlie sheet which ''^^■.'" aenal 



11 - 1 I 1 • • • 1 • -I navigation. 



IS to suspend the weight attached to it, in its horizontal path 



through the air, must present a slightly concave suri'ace in 



a small angle with the current, this f.rinciple can only be 



used in the lateral extension of the sheet; aad this most 



effectually prevents any roiling of the macliine from side to 



bide. Hence, the section of the inverted parachute. Fig. 2, 



may equally well represent the cross section of a sheet for 



aerial navigation. 



The principle of stability in the direction of the path of Piinriple of 



the machine, must be derived from a different source. Let stabviuy ui di- 

 recting the 

 A B, Fig. 3, be a longitudinal section of a sail, and let C path of the mA- 



be its centre of resistance, which experimeat shows to be ^'''"^* 

 considerably more forward than the centre of the sail. Let 

 C D be drawn perpendicular to A B, and let the centre of 

 gravity of the machine be at any point in that line, as at 

 D. Tiien, if it be projected in a horizontal path with ve- 

 locity enough to support the weight, the machine will retaia 

 its relative position, like a bird in the act of skimming; for, 

 drawing C E perpendicular to the horizon, and D E paral- 

 lel to it, the line C E wiM, at some particular moment, re- 

 present the supporting power, and likewise its opponent the 

 weight ; aad the line D E will represent the retarding 

 ])0wer, and its equivalent, that portion of the projectile 

 force expended in overcoming it: hence, these various pow- 

 ers being exactly balanced, there is no tendency in the ma- 

 chine but to proceed in its path, with its leuiaiuing portion 

 of projectile force. 



Tlie stability in tiiis position, arising from the centre of Remarkable 



* A verj' simple exj^erinient will show the truth of ;bis theory. Take 

 a circtiUir piece of writing pjl>er, and folding uj) a small portion, in the 

 line of two radii, it will h- formed into an obtuse cone Place a small 

 weight in the apex, and lei:ii!g it fall from any height, it will steadily 

 j)reserve that pi<sition to the ground. Invert it, and, if the weight \>^ 

 lixedj like ih'j Lt-lt bi;;it, it r ghts itself instanLly, 



Q 'i y-ravify 



