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ÆROSTATION. — It is announced in the Parisian papers that M. Garnerin is fitting up a balloon at the Ecole Militaire which will accomplish the desideratum of navigating the air in any direction at the will of the æronaut. On each side of a boat (which serves for car) are placed four boards something like the sails of a windwill [[windmill]], which Mr. G. moves by the assistance of a machine in the interior, "the secret of which is known only to himself." The resistance made by the air when struck by one of the boards "acts upon the balloon and carries it forward like a bird flying. Mr. Garnerin has already made several essays, which have been completely successful."

This statement is nothing better than downright nonsense. It has been more than once demonstrated, a priori, that the control of a balloon in the manner here described is impossible. Among scientific men the idea ranks only with such projects as the quadrature of the circle, or the doctrine of perpetual motion. It is more than possible that the machinery here spoken of is the same as that of Mr. Green, the London æronaut, by means of which that ingenious gentleman proposes, not to direct the horizontal course of his balloon, but merely to regulate its elevation. It is composed o two fans, or blades of wood, attached to a spindle which passes through the bottom of the car. The fans are of one longitudinal piece, to the centre of which the spindle is fixed, in the fashion of a windmill, with but two winds or arms, their blades presenting a given angle horizontally, in which direction they move. A London paper describes the effect as follows.

"A miniature balloon of about three feet diameter, was filled with common coal gas; to this were attached the hoop, netting and car, and in the car a small piece of spring mechanism was placed, to give motion to the fans. The balloon was then balanced; that is, a sufficient weight was placed in the car to keep it suspended in the air, without the capacity to rise or inclination to sink. Mr. Green then touched a stop in the mechanism, which immediately communicated a rapid rotary motion to the fans, whereupon the machine rose steadily to the ceiling, form which it continued to rebound until the clock-work had run out. Deprived of this assistance, it immediately fell. The reverse of this experiment was then performed. The balloon was first raised into the air and then balanced. A similar motion was imparted to the fans, the action of which in this case was, however, reversed, and the balloon was immediately pulled down to the ground by their forces.

A more interesting effect still was then exhibited. The balloon, with the guide-rope attached to it, was balanced as before, the guide-rope having a small brass weight fixed to the end of it. The fans were then removed from under the car and placed sideways upon it, by which their action became vertical. Upon motion being communicated, the balloon floated in a horizontal line, dragging the guide-rope after it, with the weight trailing along the floor, and continued to do so until the mechanism ceased, when it immediately became stationary again. These experiments were frequently repeated with complete success."

The guide-rope here mentioned is an invention very fully described, by Mr. Green himself, in the March number of the "Polytechnic Magazine." It is another aid in the attempt at regulating elevation — a very material point. There are many causes continually in operation to exhaust the gas in an ascension — but none is more potent than the variation of distance from the earth. When the balloon gets up very high, into a rare stratum of atmosphere, the gas is excessively expanded and must be let off to prevent explosion. Meeting then with a cloud, the silk and cordage become saturated with moisture, and the whole machine falls with rapidity. Ballast must be thrown over — and to remedy this evil, is a very long cord, wound upon a windlass, and with several small buckets at its lower extremity, so contrived as to act