_The Aërial Wave Screw operates also upon Water._--The form of screw just described is adapted in a marked manner for water, if the blades be reduced in size and composed of some elastic substance, which will resist the action of fluids, as gutta-percha, carefully tempered finely graduated steel plates, etc. It bears the same relation to, and produces the same results upon, water, as the tail and fin of the fish. It throws its blades during its action into double figure-of-8 curves, similar in all respects to those produced on the anterior and posterior margins of the natural and artificial flying wing. As the speed attained by the several portions of each blade varies, so the angle at which each part of the blade strikes varies; the angles being always greatest towards the root of the blade and least towards the tip. The angles made by the different portions of the blades are diminished in proportion as the speed, with which the screw is driven, is increased. The screw in this manner is self-adjusting, and extracts a large percentage of propelling power, with very little force and surprisingly little slip. A similar result is obtained if two finely graduated angular-shaped gutta-percha or steel plates be placed end to end and applied to the water (vertically or horizontally matters little), with a slight sculling figure-of-8 motion, analogous to that performed by the tail of the fish, porpoise, or whale. If the thick margin of the plates be directed forwards, and the thin ones backwards, an unusually effective propeller is produced. This form of propeller is likewise very effective in air. CONCLUDING REMARKS.