198 On Aerial Navigation. 



The following statement of every thing important which has 

 been suggested on this point, with some new views, is offered 

 for the purpose of facilitating further inquiries. 



Vertical Motion. 



1. The balloon being inflated with hydrogen, descends by 

 letting out some of the gas, and ascends again by throwing out 

 ballast. To this method it is a radical objection, that the means 

 of alternate ascent and descent are very soon exhausted. 



2. The air in the balloon being expanded by heat, the vertical 

 motion is produced by increasing or diminishing the quantity of 

 fuel. To this method it is an objection, that the fuel will ulti- 

 mately be exhausted ; also, if common air be used, the balloon 

 must be of very large dimensions to support tile car ; and if the 

 air be hydroiren, the expansion by heat is attended with the 

 greatest danger. 



3. The balloon being inflated with hydrogen, another issuspended 

 below the car, and into this the circumjacent air is forced by an 

 easy mechanical contrivance, and is let out again at pleasure. 

 By these means the machine descends upon increasing the den- 

 sity of tlie air, and ascends upon restoring it to its former state. 

 This method is worthy of peculiar consideration, not being liable 

 to the former objections, and being analogous to that contri- 

 vance of Nature, by which fishes sink at pleasure, and rise again 

 to the surface. 



Lateral Motion. 



1. The most obvious method of producing a lateral motion 

 is by taking advantage of the winds. These are : occasional 

 winds; trade Avinds between the tropics; the land and sea breezes 

 which in warm climates set from and towards the shore by day 

 and night alternately; the superior currents of air, which often 

 proceed in a direction contrary to those below ; and the breezes, 

 which commonly follow the direction of every river. To these 

 aids we may also add the remarkable plipenomenon observed by 

 all aerial navigators, viz. that the balloon sinks lower than 

 usual when over water, and that it has a tendency to keep the 

 direction of a river. This circumstance may partly be attributed 

 to the wind following the current, but principally to the specific 

 gravity of air impregnated with aqueous vapour being diminished, 

 and the tendency of the machine to the point of least gravity. 



2. The very ingenious proposal lately made, of directing a 

 balloon like t'^e tacking of a ship, by means of an inclined plane, 

 is worthy of much consideration. It is obvious that the addi- 

 tional weight of an inclined plane may be avoided, by forming 

 the balloon of some figure not a sphere : thus, for instance, it 

 may be an oblong spheroid, whose major axis is kept inclined at 



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