The object proposed in the construction of the Machine which is here presented to the public view, is simply to illustrate and establish the fact, that, by a proper disposition of parts and the application of a sufficient power, it is possible to effectuate the propulsion or guidance of a Balloon through the air, and thus to prepare the way for the more perfect accomplishment of this most interesting and desirable result.
In the contrivance of this design, one of the first effects aimed at was to reduce the resistance experienced by the Balloon in its progress, which is greater or less according to the magnitude and shape of its opposing surface.
To this intent is the peculiar form of the Balloon, which is an Ellipsoid or prolate spheroid, the axis of which is twice its minor diameter; in other words, twice as long as it is broad.
By this construction the opposition to the progress of the Balloon in the direction of either end is only one half of what it would be, had it been a Balloon of the ordinary spherical form and of the same diametrical magnitude.
For the exact determination of this proportion we are more particularly indebted to the researches of Sir George Cayley, a distinguished patron of the art, who, a few years back, instituted a series of experiments with a view to ascertain the comparative amounts of resistance developed by bodies of different forms in passing through the air; the results of which he communicated to the world in an essay first published in the Mechanic's Magazine, and afterwards in a separate pamphlet.
According to these experiments it appears, that the opposition which an ellipsoid or oval (of the nature of the Balloon, if we may so call it, in the model) is calculated to encounter in proceeding endways through the atmosphere is only one-sixth of what a plane or flat surface of equal area with its largest vertical section, would experience at the same rate; while the resistance to the progress of a globe, such as the usual Balloon, would be one third of that due to a similar circular plane of like diameter: shewing an advantage, in respect of diminished resistance, in favour of the former figure, to the extent we have above described; an advantage it enjoys along with an increased capacity for containing gas—the cubical contents of an ellipsoid of the proportions here observed, being exactly double of those of an ordinary Balloon of equal diameter, and consequently competent to the support of twice the weight.
