A E R 



A E R 



wiffht te ralfed or lowered by merely increafnig or diminifli- 

 ing the fiie in tlie lower balloon. Wings or oars feem to 

 have contributed little to the eft'ciSt of e tlier i-aiilng or low- 

 ering balloons. 



Many fchemes have been propofed for direfling the ho- 

 rizontal motion of balloons, borne have thought of an- 

 nexing fails to a balloon, in order to give it the advantage of 

 the wind ; but to this propofal it has been ohjefted, that 

 as the aeroilatie machines are at reft with refpcdl to the air 

 that furrounds them, they feel no wind, and confcquently 

 can derive no benefit from the fails. An ingenious writer 

 obferves, that the caCe of vcfTels at fea is qi;'te different 

 from that of balloons ; bccaufe the former move with a 

 velocity incomparably lefs than that of the wind impelling 

 them, on account of the ri> (Isnce of the water; and 

 therefore, the difference between the velocity of the wind, 

 and that of (liips, oceafions tliat ftrcam of air which afts 

 upon the fails. But a balloon, finding no refiftance, ac- 

 quires the fame velocity with the furrounding air, and 

 therefore can feel no wind. The fame author adds, that 

 the moft rational projefts for direfting an aeroftatic machine 

 are thofe wliich propofe to exert a force againft the ambient 

 air on one fide of the machine, fo as to move it in the oppofite 

 direction. Oars and wings are the only inftiuments that 

 have been ufed for this purpofe with any meafure of fuc- 

 cefs ; but farther experiments are neceflary to afcertain 

 their effeft. If wings or oars be ufed, the beft method of mov- 

 ing them is by the immed ate application of human power, as 

 in the cafe of the oars of boats on the water. Howeverthey 

 iliould be as large and light as poflible ; and they may be 

 made of filk ftretched between wires, tubes, or fticks. If 

 they are flat they mull be turned edgeways when they 

 are moved in the direftion of the balloon's courfe, and flat in 

 the oppofite direftion. One of the wings, ufed by Mr. 

 Blanchard, is reprefented \nji<;. 9. That ufed by Mr. Lu- 

 jiardi confided of mary fillc Ihutters or valves ABC D, DE 

 C F, &.C. (Jig. 10.) each of which opens only on one fide, 

 viz. A D B^C upon the hnc A B, D E C F upon the 

 line D C, &c ; and by this conftruAion, it becomes unne- 

 ceflTaiy to turn thefe oars edgeways. One of the wings, 

 conilruAcd by Zambeccari is exhibited in fig. \ i, and is no- 

 thing more than a piece of filk ftretched between two tin 

 tubes fet at an angle ; and fo contrived as to turn edgeways 

 of themfelves, when they go in one direftion. Fig. 12. 

 reprefents one of the wings ufed by Meflrs. Roberts, in 

 the voyage of September 19th, 1784. The greateft effeft 

 produced by the wings of an aeroflatic machiiie was that 

 which occurred in this voyage. It is not difficult to deter- 

 mine what force is neccffary to move a given machine in the 

 air with any propofed velocity. Dr. Hutton found, from 

 accurate experiments, that a globe of 6| inches in diame- 

 ter, and moving with a velocity of 20 feet in a fecond, fuf- 

 tains a refiftance from the air, which is equal to the weight 

 or prefTure of one ounce avoirdupois ; and that with diffe- 

 rent furfaces and the fame velocity, the rcfiftances are di- 

 reftly proportional to the furfaces nearly ; and alfo that,- 

 with difl^erent velocities, the refiftances are proportional to 

 the fquares of the velocities nearly. By thefe data the re- 

 fiftance to move a given balloon with any velocity may be 

 afligned. Let the balloon be 35 feet in diameter ; then if 

 it moved with the velocity of 20 feet per fecond, or ahnoft 

 14 miles per hour, it would counteraft a refiftance equal to 

 371 pounds ; with a motion of feven miles an hour, the re- 

 fiftance would be 68 Tjounds ; and at three miles and an half 

 in an hour, the refiftance would be 17 pounds ; and fnch is 

 the force with which the aeronauts muft aft on the air in a 

 contrary diredion, in order to communicate fucli a degree 



of motion to the machine. If tlie balloon move thro\igh a 

 rarer part of the atmofphf re than that at the furface of the 

 earth, as 3d or Jth, fee. rarer, the refiftance will be lefs in 

 the fame proportion ; yet the force of t!ie oars will Ve di- 

 minilhed as much ; and therefore the fam.e difficulty re- 

 mains. It may be <>bi'ervcd in general, that the aeron?Ht 

 muft rtrike the air, by means of his cars, with a force juft 

 equal to the refiftance of the air or the Ipalh-on, and there- 

 fore he muft ftrikc that air with a velocity wbii h muft be 

 greater as the fuiface of the oar is lefs than the refiftid fur- 

 face of tile globe, but not in the fame proportion, becaiife 

 the force is as tlie fquare of tlie velocity. Kupi'ofi. that the 

 aeronaut afts witli an oar equal to 100 fquare feet of fur- 

 face to move the balloon above-mentioned at the rate of 

 20 feet per fecond, or 74 miles an hour, then he muft 

 move this oar with the great velocity of 62 feet per fecond, 

 or nearly 43 miles an hour : and fo in proportion for other 

 velocities of the balloon. Hence it is highly probable, 

 that it will never be in the power of man to guide fuch 

 machines with any tolerable degree of fuccefs, cfpceially 

 when any confiderablc wind blows, which is generally the 

 cafe. A helm feems to have no particular power in direft- 

 ing the courfe of a balloon, for the fame reafon that has 

 been alledged to evince the inefficacy of fails. We have 

 not in air, as in water, fays count'de Mirabeau, in his Con- 

 fiderations on the Order of Cincinnatus, the refource of a 

 fixed point of aftion upon a fluid, which has alfo much 

 greater refiftance than air. He adds, that as there are dif- 

 ferent currents of air, fometimes in oppoiite dircftions, and 

 balloons are capable of afcending and defcending in fearch 

 of thefe currents, this circumftance may favour the hope of 

 direfting aeroftatic machines. Perhaps, an attention to the 

 means by which birds fly againft the wind, added to obfer- 

 vations of comparative anatomy upon fifties and birds, which 

 furmount the currents of the two fluids that are common 

 to us and them, may alfo fugj^eft new ideas with refpecl to- 

 the direftion of balloons. Time alone, and ncmerous ex- 

 periments, can bring thefe rtfleftions to maturity, and rea- 

 hze the expeftations fuggefted by them. 



Several of the foreign journals have lately announced an 

 invention of profeftor Danzel for direfting an air-balloon 

 through the atmofphere. W^ith this view he hasconftiiiifted 

 two cylinders, or axles, to the ends of v.hich are fixed, in 

 the form of a crofs, four fails, or oars_, moveable at the point 

 of their infertion in the cylinder, in fuch a manner, that 

 when made to move round by means of a liandle, the eight 

 oars, like the cogs of a water-mill wheel, prefent fucccflivcly 

 to the air fometimes their flat fide and fometimes their 

 edge. To caufe each oar to turn back on itfelf about the 

 fourth part of a circle, M. Danzel has not only left fufiici- 

 ent play at the point where the ftiek of each oar is infertcd 

 in the cyhnder, but has placed the ftick in fuch a manner 

 that the air itfelf makes the oar fall back, at each turn, with 

 the neceftaiy velocity and precifion. Each of the two cylin- 

 ders, armed with its four oars or fails, is deftined to occupy 

 one fide of the balloon, with its four oai-s on each fide. For 

 a farther account of this apparatus and of its efTcft, fee 

 Philofophical Magazine, vol. iv. p. 108. 



As parachutes, in the form of umbrellas, have been pro- 

 pofed in order to guard againft accidents, and to break the 

 fall in cafes of fudden defccnt, we fliall here annex a method 

 of eilimating the power of fuch defenfive machines, A 

 perfon, moving uniformly at the rate of ten feet per fecond, 

 may defcend \wth fafety. For this uniform defcent the re-- 

 fiftance of the air muft be equal to tlie whole defcending 

 weight. Ruppofe then that the weight of the aeronaut is 

 J50 pounds, and that tlie parachute i$ flat and circular, and 



made 



