A paper read at the Society of Arts on Wednesday, Feb. 15, 1899; Captain Baden Powell, Hon. Secretary to the Aeronautical Society of Groat Britain, in the chair.

In the first years of the century, the Russian Academy organised, at St. Petersburg, what may be regarded as the earliest balloon ascent for genuine scientific research. One chief object which they had in view was to determine any difference in conditions existing at various altitudes above plain country as compared with those observed by Humboldt, Saussure, and ethers a t like elevations on mountain heights, and that this is even still an important line of inquiry for which balloons are eminently well suited, I shall hope to make sufficiently clear. The experiments proposed, which, to–day, read quaintly suggestive', were to include an investigation of the power of solar rays, of the existence of electric matter, and of the intensity of the colours of the prism. No results of consequence, however, were obtained.

The principle of this invention consists in giving lateral motion to balloons by utilizing the resistance of the air, during successive ascents and descents, by means of a large triangular sail, placed between the bag and the car at an oblique angle with the horizon; and in rotating them at will by means of a smaller rudder–sail, which is capable of turning on a horizontal axis. The sails are constructed to furl readily.

The principle was first applied to a buoy, depressed to the bottom of a running stream. As it rose it could be made to turn in either direction, according to the setting of the rudder, and would proceed in a course opposed to the stream if thus directed, and all by passive means. When weighted it would act similarly during descent. On removal of the weight, it would continue its course whilst re–ascending, and so on. Anyone can experiment for himself, at a trifling cost, in this way.

How birds fly, and what is the force employed to sustain and propel them, has been so often discussed that most would think the subject exhaustively explained and thoroughly understood. Yet it is doubtful whether such is the case, seeing that many now are inclined to ascribe the phenonemena of forward flight to the curvature of the surface of the wing. Another view, and a nearly opposite one, is this, that the wing's chief function is that of sustaining, and has but slight propelling property, and what propelling power the curvature of the under surface endows the wing with, is exerted in giving a forward course to the wing itself in its descent; this is the view that will be sought to be worked out in this paper.