Two practical applications of the gyroscope have been recently suggested, namely, the steadying of vessels, and the balancing of railway trains running on a single rail. Now a third possibility of utilizing this interesting Instrument is discussed by C. L. von Llllenbach in La Conqu te de l'Air. As the gyroscope has been found to insure the stability of the two kinds of oscillating vehicle referred to, it might be employed as well in connection with vessels sailing through the air. In this connection it should prove the more valuable, as lack of stability is known to constitute the greatest drawback to the use of the aeroplane. After suggesting that some kind of gyroscopic apparatus may be used in the Wright aeroplane, the author points out the great analogy between the conditions affecting the stability of aeroplanes and the stability of a “monorail” car. In both cases the center of air pressure and the center of gravity must fall on the same straight line if the vehicle is to preserve its balance. However, it is very difficult to obtain this coincidence at the right moment and within the limits actually desired, which is the most Important point in connection with aeroplane flights. Neither reflex rudders, nor the use of automatic sliding weights, nor finally the front and side steering gears, have given full satisfaction in this connection. A more efficient method of obtaining the desired stability consists in arranging the supporting surfaces in pairs behind one another, the practicability of this principle having been demonstrated by Prof. Langley. A similar system has been recently employed in France by Blerlot. According to Llllenbach's suggestion, the gyroscope could be used in steadying the aeroplane. This would prove valuable, not only in connection with ordinary aeroplanes, but even with the Langley double-aeroplane airship. Flying machines of the latter type, to which most experts ascribe the best chances of final success, possess a great stability in mid-air by sliding like sleds on an air cushion, so that only linear inertia has to be accounted for. They will accordingly require the addition of a gyroscope utilizing rotative inertia only in the case of slow flight, in starting and landing, and during storms. In any case the gyroscope would augment the safety of the flight by fixing the center of gravity of the apparatus, thus exerting a favorable Influence On the speed of the motor. In fact, the axial position of the gyroscope seems to be of no importance, for, by reason of its vertical or horizontal rotation, it offers a uniform resistance only to a lateral displacement of the apparatus. It may be said that propellers possess a certain gyroscopic action, especially if the axis is short. The blades of the screws should obviously be thin and of especially light material, on account of the centrifugal force. The propeller actuating the aeroplane thus contributes, by its rotation, to Increase the stability of the airship, and when there is only one propeller, a slight tendency to rotation of the airship in an opposed direction will be observed. Two propellers rotating in opposite directions, however, compensate each other, and can be arranged either on the same shaft behind one another or symmetrically, side by side. Th former construction is more simple, since the other requires a rigid transmission; the latter, however, is the preferable. Von Llllenbach suggests arranging with three or four pairs of very slightly curved vanes, two additional pairs of symmetrical propellers, a separate motor, and a dovetail. In order to Increase the stability of this arrangement a gyroscope should be added. It should be said that an Austrian and a German inventor a few years ago suggested the use of gyroscopes in connection with airships, and that a similar idea has been patented by Etrich and Wels, but abandoned during construction. The subject of the application of the gyroscope to the aeroplane has been discussed both in the columns of the SCIENTIFIC AMERICAN and SUPPLEMENT. The direct application of jets of dry steam to a gravel bank through the agency of driven pipes has been found to be an efficient method of thawing frozen gravel.