332 ON THE VARIOUS MODES OF FLIGHT 



the burning' of vine twigs under it. The Montgolfier or fire balloons, as they 

 were called, were superseded by the hydrogen-gas balloon of MM. Charles and 

 Robert, this being, in turn, supplanted by the ordinary gas balloon of Mr. 

 Green. Since the introduction of coal gas in the place of hydrogen gas no 

 radical improvement has been effected ; all attempts at guiding balloons have 

 signally failed. This arises from the vast extent of surface wliich they neces- 

 sarily present, rendering them a fair conquest to every breeze that blows ; and 

 because the power which animates them is a mere lifting power which, in the 

 absence of wind, must act in a vertical line, all other motion being extraneous 

 and foreign to it. It consequently rises through the air in opposition to the law 

 of gravity, very much as a dead bird would fall in a downward direction in 

 accordance with it. Having no hold upon the air, this cannot be employed as 

 a fulcrum for regulating its movements, and hence the cardinal difficulty in bal- 

 looning as an art. 



An}'' one attempting to control the movements of a balloon is very much in 

 the position of a boatman who endeavors to steer his craft, which is drifting 

 with the current, by pushing against the stern. 



If ever the balloon is to be utilized as a means of transit, this will probably 

 be achieved by converting part of its lifting power into a horizontal propelling 

 power, which possibly could be done by affixing a horizontal screw, like a small 

 windmill, to the car; this apparatus receiving its motion by being forced against 

 the air from beneath during its ascent, (the air playing upon it from above,) and 

 communicating its movements to a similar and smaller screw placed vertically 

 or at right angles, which could be made to revolve with great celerity as a 

 driving screw. To prevent rotation in the balloon itself, it might be armed with 

 j)lates of some light material placed at right angles to the plane of rotation. 

 The great expense, however, involved in the construction and filling of the bal- 

 loon will alwa^-s operate against its being used otherwise than as a luxury; 

 while the enormoiis expanse and delicacy of the material employed, as well as 

 the change in volume of the contained gas arising from increase or decrease of 

 temperature, cannot fail to prove troublesome, not to say dangerous. 



Finding that no marked improvement has been made in the balloon since its 

 introduction in 1782, we naturally turn our attention to some other method of 

 traversing the air; and here I would add my independent testimony in favor 

 of the heiice or screw, not only as a lifting power, but also as a pro})elling power. 

 When I commenced my inquires into the structure and the uses of wings, I was 

 early struck with the curious manner in wliich the}' are twisted upon themselves, 

 and how they are rotated on and off' the wind during flexion and extension, after 

 the manner of screws; and without knowing (for the subject of artificial flight 

 is not much in my way ) that the heiice had been proposed as a means for raising 

 inanimate bodies, I had actually constructed a double screw, with a view to test- 

 ing its efficacy in this respect.* I have therefore unwittingly laid anatomy and 

 j)hysiology under contril>ntion in support of what I find is not a new doctrine.t 

 I was impelled in this direction hy detecting the principle in nature, and from 

 knowing that a body to rise and progress in the air need not necessarily be 

 lighter than it; in fact, that the balloon is constructed on a principle diametri- 

 cally opposed to that on which the bat, insect, and bird are constructed, and is 

 from this circumstance open to serious, and in some respects, insuperable objec- 

 tions. 



The efficacy of the screw in water is well known, and the action of the child's 

 toy, usually called the spiralifer, will illustrate its utility as applied to the au\ 

 This to}"-, for toy it has hitherto been, consists of two inclined planes, produced 



* This screw had tour fans or blades, two of which revolved from left to right ; the remain- 

 ing: two from right to left. This I found to be necessary to prevent rotation in the driving 

 apparatus, whicli consisted of a steel spring and clockwork. 



tl'auctou, the engineer, predicted the future importance of the screw in aerial navigation. 



