O G., of Mich.—For steamers under a certain length, it would be a potitive loss to apply more than two wheels; but steame s of a great length-double the length of our largest at present—may yet be built, and for them four wheels may be much better than two Much of the water-lift is due to the partial vacuum formed by paddle wheels aBthay resolve. We do not make models. L P. II., of Vt—The very same objection to the ordinary brake has been complained of before, and almoat precisely the same remedy as you propose has been advanced, but we believe a patent was never issued upon it. We do not think you could obtain a patent. J. N.. of Ohio—Your speciBcation came to hand properly executed, with the necessary fees to pay for an engraving, which will appear in a week or two. T D, L,, of Tenn.—Much obliged to you for the subscribers you sent us, but are sorry to inform you that we have not a copy of Prof. Silliman's speech with which to furnish you. J. C, of Va—Car wheels have been constructed with an axle for each wheel ; they hare been illas trated in our baok volumes ; they do more harm than good, as each wheel seeks to move independently on a straight line. Water engines are now in use in some places. The quick motion of the valvescan be obtained by cams ; the old tappet motion (by levers) worked valves as suddenly or slowly as was desired. G W. L , of Va—The prussiate of potash is the substance employed for case-hardening. The journals, however, will oxydize afterwards if exposed to moisture and the atmosphere, W. F, of Mass.—An electro-magnetic engine is not strictly self-acting, as you require a battery for the electro-magnets. Many machines of the same character, but not of the same form, have been presented to as, and some have been patented- Yours affords no ground on which to base a good claim for a patent. T. J. H., of Va.—The work you wantis Morfitt's Applied Cnemistry, sold by H. C. Baird, of Philadelphia. D. P. M., of O.—It is surprising that a man of your intelligence and mechanical ability should know no better than to spend your time and money in so fallacious a scheme as trying to invent perpetual motion. D. D., of N. C—The pressure on the piston is ge-nerally about one pound less than that on the safety valve, when the steam pipe is well covered and the throttle valve full open, M. T., of Phila.—There would be more lost than saved by your second paddle-wheel. Money received on account of Patent Office business for the week ending Saturday, Aug 6:— T. D., of Ala., $20 ; W. P., of L I, $30 ; D. E-McD , of Mass , $50 ; C. H. W., of Ohio $20 : H F. B , of-----, $55 ; D. D., of N. Y., $14 ; S. T, J., of N. Y, $80: T. T J . of Pa., $25 ; S. B. D , of Mich., $30 ; D B. M., of N Y., $27 ; J. B. E , of N. Y., $55 ; S. M., of 111., $20 ; W. T. M., of N. Y , $30. Specifications and drawings belonging to parties with the following initials have been forwarded to the Patent Office during the week ending Saturday Aug. 6:- S. B. D., of Mich. ; N. B. P., of 111. ; T. T. J., of Pa.; D. D., of N. Y.; J. N., of Ohio ; W. T. St., of N. Y.