j(4 On the prefent State of Aerojlation. 



lations the car became (in Garnerin's experiment) on a line 

 with the horizontal axis of the machine, (or, in other words, 

 the point of fufpenfion,) the force of gravity, or the gravitating 

 power of the weight in the car, on the umbrella, being at that 

 crifis reduced to nothing, the flighteft caufe might have car- 

 ried the body of the machine in a lateral diredion, reverfing 

 the concavity of the umbrella, and Mr, Garnerin, perhaps, 

 have fallen upon the now convex yet internal portion of the 

 bag, and the whole have defcended confufedly together *. 



I fliould 



• The umbrella being afted upon in a perpendicular direction from the 

 car, if by any, the moft trivial caufe, the latter vibrates from the perpendi- 

 cular it will draw the machine in the fame inclined direction ; the car alfo 

 ■with its cords of fufpenfion, now adting the part of a pendulum, will con- 

 tinue to ofcillate to each fide till a perftft cijuilibrium is reilcred. The 

 fpace of the arc defcribtd in each vibration will depend upon the diftancc 

 between the car and the parachute conjunctly with the refiftance afforded 

 bv the latter to tht air, whereby on decreafing the refiltance (or, which 

 js the fame thing, the furface of the umbrella,) the weight in the car will 

 fooner draw the machine into the perpendicular, and the ofcillations con- 

 ■fequently ceafe :. thus a pirachufe whofe fuvface is fmall enough to obviate 

 ofcillations in the middle regions (/. e. the half of the ufual heights fur- 

 ir.ounted in aeroftatic experiments, or about 5000 feet), would be defec- 

 tive for want of furface to moderate the velocity of defctnt when near the 

 ground, and -jiceveyfa: if, therefore, we can augment or diminifh at plea- 

 fure the furface and confequent refiftance of the parachute during its de» 

 fcent, we Ihall have attained the perfe61ion of the machine. 



Thus in Mr. Garnerin's experiment the olcillaiions did not commerce 

 till the machine felt the increafed refinance of a more denfe zone of the 

 atmofphere; and having then no means of diminifhing the fame, the vibra- 

 tions began, continued, and incrtafed, till, by arriving in a yet mote denfe 

 region, a greater rtfiflance was oppofed to the ofcillations cf the bafket, 

 gradually diminifhing the arc of the fame to nothing, this alfo being af- 

 fifted by t difcharge of ballad from the car, by which means the weight of 

 the pendulum arid its power to fwrep through a de/fe atmofphere were 

 conjointly diininifhed ; for the "jibraiion of a poidulum lutil be i>i proportion 

 to in length, and alfo to the denfty of the medium through lubich it is to 'vi- 

 brate; a fr.ft too much overlooked. There is therefore a medium height 

 at which the ofcillations will be the greateft ; and the diftance of this me- 

 dium frcrn the earth's furface will vary with the difftrent ftates of the ba- 

 rometer at the earth ; or, in other words, as the denfity at diflferent heights. 

 Thus, when the altitude of an aeronaut defcending by a parachute is great, 

 the atmol'phere is there too much rarefied to occafion refiftance to the um- 

 brella fufticient to allow of an ofcillation ; but when in a lower zone a vi- 

 bration has unfoitunately begun, the atmofphere is here too denfe to allow 

 of that velocity of dcfcent wjiich only cculd have prevented the commence- 

 ment of the ofcillations, yet rot denfe enough to afford fufficicnt refiftance 

 to retard the fwcep of the baflttt ; while in a yet more denfe region, nearer 

 to the furface of tht garth, the air affords fo much refiftance to the fwing 

 of the car, as foon effc£tv>aMy to ftop the fame, cfpecially if the weight 

 therein could now be diiiiiniincd by a difcharge of balkft ; a faft evinced 

 jn Mr. Garnerin's experiment, when he threw out a quantity of ballaft 

 -.vh';n near tlie caith to moderate the ihock of his defcent, which imme- 

 diately 



