The following account of the principal of these pad dle wheels is given by Dr. Lardner, who has instftuted experiments with them, compared with the common wheel, and has found the results to coincide satisfac torily with those which he has deduced from mathe matical calculation : "The consequence of the combination of the mo tions of the paddle boards and the wheel is, that the edge of every paddle board is always presented to the highest point of the wheel, as shown in Plate DX. Fig. 9. The entire action of each board, perpendi cular to its surface, being revolved into two actions, one horizontal and the other vertical, the proportions, quantities, and directions of these actions will be seen at once, by observing the sides of the several parallel ograms in the figure and the directions of the arrows. One peculiarity which this presents, and in which it differs most strikingly from other wheels, is, that all the horizontal arrows point in the same direction, in dicating that all the horizontal elements of the forces of the boards act in the same direction, and that they, therefore, can be made to propel without any back ac tion whatever. It will also be observed, that the ver tical elements, which, on the one side of the vertical diameter lift, and on the other side depress, are much smaller in proportion to the whole force than in the common wheels, see Fig. 10. and therefore the force expended without any useful effect is much less in pro portion to the whole force in these than in the com mon wheel.
A wheel of this kind having no back action, might be totally immersed, and would still continue to propel. In consequence of the diminution of the lifting and depressing efforts, or what is the same, of the degree of the feathering principle with which it is endowed, its motions through the water is smooth, and attended with but little agitation, and is, therefore, the more effectual as an impellent power." Among the ingenious contrivances for propelling steam-boats, we must mention that of Mr. Gladstone's of Castle Douglas, who has proposed to have two wheels on each side, with a chain of float boards be tween them, as shown in HYDRODYNAMICS, Plate CCCXX. Fig: 6, float boards or paddles being substi tuted in place of the buckets C, F. The two wheels A, 13, are of course placed so that the line joining them or the direction of the line of paddles is a little inclin ed to the horizon. Such a construction has great theo retical advantages ; but the looseness of all the parts has, we believe, been the cause of its failure in practice.
A method of propelling steam-boats without wheels was proposed and carried into effect in 1820 by J. B. Fraser, Esq. and G. Lilly, Esq. who took out a pa tent for the invention. The method consists in forcing out from the stem of the boat a small jet of water by means of compressed air. M. Bernouilli was, we be lieve, the first who suggested the idea of propelling boats by this means. He proposed to fix on the boat
an upright bent tube like the letter L, the vertical part having a sort of funnel top convenient for filling the tubes with water, which, descending through the ho rizontal part, and issuing at the middle of the stern, and below the surface of the water, propels the boat by the reaction of the effluent stream. Dr. Franklin': proposed an improvement upon this method, which consisted in adding another tube of the form L. " The two standing back to back, the forward one being worked as a pump, and working in the water at the head of the boat, would draw it forward while pushed in the same direction by the force of the stern. And after all, he adds, it should be calculated whether the labour of pumping would be less than that of rowing. II fire engine might also in some eases be applied in this operation with advantage.'' Dr. Franklin next proceeds to show how the boat might be propelled by the use of air in place of water, and he suggests the use of an air vessel with proper valves to permit the force to continue while a fresh stroke is taken by the lever.
The apparatus described in Mr. Fraser and Mr. Lil ley's patent consists of a cistern or condensing reser voir placed near the bow. From this cistern there descends a main tube, with a plug that may be opened and shut at pleasure. Two tubes, each of them having a plug, branch off from the main tube, and extend to a point rather nearer the how than the centre of gra vity of the vessel. From these two tubes the water issues in propelling the vessel. The main tube, how ever, continues to extend till it reaches a point about one-third of the length of the boat from the stern, and • then divides into two tubes, which are bent back so as to open towards the bow of the vessel. The water is made to issue from these tubes in order to repel the vessel or give it stern way ; other tubes branch off from the main tube before the two first, two going to the bow and two to the stern of the vessel, and they are put at right angles to the keel, one of each pair being directed to one side, and the other to the oppo site side of the vessel. The plugs of these tubes are united transversely, so that either pair being opened the water may issue near the bow on one side of the keel and near the stern on the opposite sidle of the keel for the purpose of turning the boat. A pump wrought either by men or by steam is then connected with one side of the condensing reservoir. A boat thus fitted up and wrought by two. men, who pulled at separate levers in the same manner as in rowing. went at the rate of three miles in an hour, though the two aper tures which discharged the water was only one-fourth of an inch in diameter each. A full account of this apparatus, with engravings, was given by the editor of this work in the Edinburgh Philosophical Journal, Vol. V. p. 120.