O. R., of Wisconsin—Wo think you had better go on with your experiments, for a great many patents have been taken out, but none have superseded the old plan. Practice alone will prove the value of your invention ; the application of the gas to the lead while in a molten state we think is new. You are the best judge of the utility of the pelvimetre, being in a position to use it ; it is a new device. We do not sell inventions or patents. U. ?. B., of Pa—There appears to be somenovel-ty in your arrangement of a railroad brake ; we ad-ve you, however, not to use a rack and pinion, as it might not prove of sufficient strength in an emergency. H. C, S., of ?. H.—The general impression we find to be contrary to our judgment ; we do not think the Ericsson applicable to small stationary purposes. J. P. M., of Vt—We think your Switch Alarm to be new, and we cannot see why a patent should not be granted ; it would be useful if made to operate well. 0. W. B, of Ohio—There appears to be some novelty in your suggestions about flying machines, but we really do not discover in them anything of a valuable or practical character to justify you in doing anything more with the matter. F. C , of N. C—We sent you Vols. 5, 6, and 7, in sheets, by mail, on the 9th inst., and credited your subscription up to the end of the present volume. S. F , of Pa —We have never seen the same plan proposed for working a magnetic telegraph by the train of cars, but a wire telegraph has been proposed to us more than once: the idea is a good one. We cannot furnish the back numbers for the present year, D. H., of Ct.—Yours has been received and will meet with attention. G. A. W , of N. 0.—We do not know of any patent on the article mentioned in your letter. J. R. G., of Va.—We have seen a shingle machine constructed upon the same principle as yours, and cannot advise YOU to make an application. V. L. 0,,of Tenn.—We see nothing in either of your inventions to justify an application for a patent; we credit you with $2 on subscription to the Sci Am. ?. ?. ? , of Ind.—We do not see any chance for a patent on the device for preventing drift wood from lodging on piers, bridges, etc. R. F,, of Pa.—We have no engine of the size you want; $5received on account of subscription. J. A, of Conn.—There is no novelty in your oil cup ; essentially the same thing was patented last year. J. R. K, of Geo.—We do not know of any article better than copal varnish for tke purjosft aamed. S ?\, of ?. Y.—No varnish is put upon the articles you mention—clock work; you must burnish up better ; a fine varnish made of clean lac, dissolved in alcohol, is excellent for covering articles that are exposed to the weather. F. S. 0., of Boston—The pressure of water increases with the velocity ; how can it be otherwise ? Multiply the weight into the velocity, and you have the momentum. Try and press the water in a close full Vessel with a velocity of 15 feet per second, and find out the resistance to satisfy yourself. W. H. P., of Mo.—The only reason we can give for your water not rising above D, is, that there must be a difference of weight in favor of the column of water to be raised in tube ? over the inlet tube ; a column of inlet water will only balance another of equal weight and no more : a tube of one inch diameter will not force watering connected tube of two inches diameter up to the same level by ite gravity : look into this closely. J. C. S , of ?. Y.—Your plan about the employ-mentof the heated gauze, for the hotairengine, is the same as that employed by Sir George Cayley, a number of years ago : practically, neither hot air, dry steam, nor heated gases answer to work machinery. The increasing pitch answers the same purpose as that which you propose in the propeller ; Ericssons patent embraced the principle of a series of blades having different velocities. R. M-, of Nova Scotia—Your insulator appears to be good, but it surely cannot be made as cheap as a glass one, and cheapness is an important item; in our opinion glass is also abetter material. H. F. S., of Pa —If we obtain the desired information you will see it in our columns. M. K., of ?. Y.—Our books are correct, the notice got into your paper by mistake. B.F.W,,of La.—We have examined the sketches of your alleged improvements in rotary steam engines, and think they embrace novely. You ask us what we think of them: to be candid—not much, and i hey can be made to operate successfully we shall be mistaken. Money received on account of Patent Office business for the week ending Saturday, March 12 :— J. B., of R t, $5; S. G. W , of ?. Y. $30; W. M. & Co , of ?. Y., $57 ; J. 0., of ? Y., $10 ; A. W. R., of $5 ; R. M. F , of ?. Y.. $30; W. H. M., of Ind., $10 ; C. P., of Mich., $20 ; H. G. DeW., of N. Y , $30; T. S , of N. Y., $25 ; L. D. of N. Y, $60 ; J. ?. ?., of ?, Y., $20 ; R. P., of Vt, $20. Specifications and drawings belonging to parties with the following initials have been forwarded to the Patent Office during the week ending Saturday March 12 : — F. H., of Pa. ; Y. S-, of N. Y.; L. K., of N. Y. ; L. ? D , of ?. ? , (2 cases) ; J ?. ?.; of Ct; R. P., of Vt; ( F. C. G., of N. Y.; C. H.P.,of N.T.