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Professor A. Crestadoro has just secured under the new patent law, an interesting scheme for propelling vessels. He considers the use of paddles or blades to be a mistake similar to that which so long prevailed in the application of locomotives on railroads, and which materially retarded the progress of that invention, when, taking for granted the inability of the plain circumference of the wheels to propel the carriage, much labor and skill had been wasted in the contrivance of levers, which acted on the road in a manner somewhat resembling the feet of the horses. Now, as the appprehen- ded insufficiency of the adhesion of the plain circumference of the wheels with the road to propel the carriage has been proved a fallacy, so he considers the necessity of paddles or blades, of whatever description they may be, as altogether fallacious and that the best and cheapest method of improving the propeller is to use simply the plain circumference of cylindrical drums. It is a natural supposition that a plain round surface should have no tractic adhesion with the water ; but on close examination it will be found that not only such is not the case, but what is even more surprising, the tractic adhesion of a plain cylindrical dram is far greater than that of a paddle-wheel ot equal size. Taking, for instance, the steam vessel Atlantic, wbose paddle wheels are ot 35 feet diameter, and length of paddles 12 feet 6 inches, supposing a moderate immersion of five feet paddles—one pair of drums of equal size at equal immersion would displace a pair of cubic segments of about 135,631 lbs. of water, or, what amounts to the same thing, a pressure of not less than sixty tons would act upon the drums as a tractic adhesion which is by tar superior to that afforded by the best method of paddle wheels in the most favorable circumstances. Now, the cylindrical propeller has the substantial advantage that it can be, when reduced to a moderate diameter, applied as well as totally immersed, if it be, (as proposed by the patentee,) fitted into a semi-cylindrical case, with only such a clearance as is just sufficient to let the drum have a proper action, the other half drum or semi-cylindrical projection being out of the case for the propelling action.— [English paper. [There is a decided mistake in the conclusions of Prof. Crestadoro. No mortal man but himself, we believe, ever would suppose that paddle wheels were invented because it was believed that broad sheathed wheels would slide on the surface; such an idea never was entertained, consequently no such mistake as that referred to was ever made in the case of steamboats. The two modes of propulsion are entirely different, the one is by traction, the other by the displacement of an incompressible fluid. Now, the action ot a rigid body passing over another rigid body, is altogether different from what it would be if propelled throngh a fluid. We have also to state that drums have been tried as substitutes for paddles, but as might be expected, proved utterly incompetent. We cannnot see how a man of science permitted himself to be led away by such an idea as that set forth in the above extract.
