S. Y. A. L.. ol D. C.—We entertain a high opinion of the philosopher to -whom you refer, but hie deductions in regard to colors are certainly behind, and not so satisfactory, as those of Newton, who deserves the most credit for his researches on this subject, although he was mistaken in many of his conclusions. A. W. D., of Pa.—Transparent window shades are prepared by a primary thin coat of white varnish. You can purchase this varnish at any store where painters' materials are sold. E. B., of N. H.—Oil made from sunflowers is used to adulterate linseed oil. The latter will make a varnish fully as transparent as the former. We have never seen a really pure white and transparent varnish devoid of smell, nor pure white shellac, but we think it may be bleached perfectly white with chlorine. G. W.,of 111. and A. D., of Mich.—You should consult your physician in reference to the treatment of yourdiseases. J. J. B. H., of Ind.—Volumes have been given to the public on the gyroscope, without adding a single golden grain to the treasury of useful knowledge. It would occupy too much space in our columns to give you the information desired on the subject. J. M. B., of Pa—Your views of the mercurial wheel are correct, but the machine you propose instead could not be made to work. G. F. G of Mich__It would not be patentable to make a roofing compound of coal tar, rosin oil and sand, with cloth next to the boards. Roofing of this character has long been known to us. E. D. T., of Pa—Galvanized iron will last as long as tinned iron, but is not so easily soldered. We are not aware of its price. Address Vandervoort & Dickerson, No. 245 Water street, this city. F. W. L.,of N. Y.—A little whiskey or the oil of cloves added to a solution of gum arabic prevents it from souring, if kept in a covered vessel. The colors on japanned wares are baked or dried in ovens constructed for the purpose. A. E. P., of N. Y—By the use of magnifying single eye glasses, some engravers have altered the focus distances of their right eyes, but the cases of long and shortsightedness to which you refer were not thus caused. P. A. P., of Fla—The idea of propelling vessels by hinged paddles suspended on sliding frames on either side is a very old one, and long since abandoned as futile. J. J. I., of N. Y—There are cases on record of persons having been blind in one eye, and not aware of the fact until informed by their physician. Your case is not a very singular one. F. &S.,ofKy.—We do not recommend the use of gum catechu for preventing incrustations in boilers where soft water can be obtained, because it contains tannic acid, which will injure the iron, if, trom any want of care, too much of it is employed. J. D. and C. H., of N. Y.—Holtzapffel's work on turning is sold by Balliere, 290 Broadway, this city. It willperhapsfurnishyou with the desired information in regard to screw-cutting on the lathe. S. Cochran, of Petersburg, Va., wishes manufacturers of grain cradle fingers and snaths, ready dressed and bent with the trimmings, to send him a list of prices. R. F., of Conn.—We made the alteration in your communication in order to express an opinion deduci-cible from the latter part of the sentence to which you refer. If you did not intend to state a fact, or express an opinion, your words were idly used. W. D. S., of N. Y__Gold solder is composed of 24 parte gold, two of silver, and one of copper. Common spelter solder is composed of equal parts of lead and tin. Gold soldering is executed with the blow pipe. Charles Meyers, of Fond du Lac, Wis., wishes to purchase a patent for the best machinery for making clothes' pins. B. G. J.,ofPa__Liquid blue is not patented. It is made by neutralizing the acid on a strong solution of the sulphate of indigo, with chalk. A precipitate falls to the bottom of the vessel ; the liquid left is a clear deep blue solution. H. T. B., of Md—If you have plenty of water on your low fall, an undershot wheel is the best you can use. We are unacquainted with the saw mill to which you refer. G. J., of Ala.—We cannot recommend you a better substance for the protection of tenons and mortises in tressle work than coal tar. Paint it upon the tenons when moderately hot, and pour it into the mortises. A B. K., of Pa__Soft buckskin or fine linen, we think, are superior to india-rubber for bullet patches. We have never heard of Sharp's rifles being liable to lead up in the grooves. L. B.. of 111.—Two engines are employed on nearly all steamships, and each wheel has the benefit of both to produce an equable motion. You seem not to be aware of this fact. J. M. ,of C. K—Up to 1847 there had been granted in this country fourteen patentB for improvements in the endless chain horse-power. The first patent seems to have been issued to Samuel Lane, of Hallowell, Me., in 1830. The endless chain power of Messrs. Wheeler, of Albany, was granted in 1841, and since that time it has been extensively used for threshing grain, sawing wood and other purposes. G. M. E., of Pa__The main cause operating against the success of a steam plow is the complication and expense attending its construction. There are many others of a minor character too numerous to be detailed here. Whether they will be overcome or not is for in-? ventors who "know no such word as fail" to deter-\ mine. 7 O. P. S., of Ohio__It is a common device to suspend \_two objects, such as water wheels, on the same shaft so ^aa to cause an equal degree of pressure to be exerted against both. Our government does not buy patent rights with a view of making them public property. D. A, M, of Pa.—We believe the vulcanized gutta percha belting is a good article. Money received at the Scientific American Office on account of Patent Office business, for the weekending Saturday, April 24,1858 :— G. S., of N. Y., $55; F. Y., of Ky, $27; J. H. H., of S. C, $30 ; W. W., of Miss., $55; J. T., of Mass., $35; T. J. B., of Ind., $25; L. P., of Del., $40; C. B. B., of HL, $25; J. C. S., of Mass., $25; S. & G., of Mich., $30; J. P.,ofTenn.,$50; H. S. F., of Mass., $30; J. H. E., of N. Y.,$60; A. A.D., of Wis.,$35; P. T. B., of 111., $30; G. N.,of Ohio, $20; E. D., of N. J., $100; T.S.,of N.Y., $30; H. B., of N. Y., $250; J. D., of Mass., $25 ; E. K, of Conn., $30 ; J. F. T., of S. C, $30; H. A. N., of Mass., $25; J. A. O., of Conn., $30; A.A., of 111., $30; S. N. C, of 111, $20; W. Y. H., of 111., $30 ; F. H. O., of Pa., $30; A. E. T., of Ohio, $30 ; N. H., of Pa., $25; E. S., of La., $20; O. S., of N. Y., $25 ; C. McJ., of N. J.,$30; J. S. M., of 111., $25; M. K.,of N. J., $25; J. P. S., of N. Y., $25; W. V., Jr., of N. Y., $25; P. C. I., of L. I., $25. Specifications and drawings belonging to parties with the following initials have been forwarded to the Patent Office during the week ending Saturday, April 24,1858:— C. B. B., of 111.; J. C. S., of Mass.; L. P., of Del.; G. S. M., of 111.; J. M. H., of Pa.; J. T., of Mass.: F. Y., of Ky.: U. & B., of Ind.; M. K, of N. J. ; H. A. N., of I Mass.; G. N., of Ohio, (2 cases;) J. P. S., of N. Y.; J. S., of L. L; W. V., Jr., of N. Y. : O. S., of N. Y^ P. C. I, of L. I; G. S.,of N. Y.; J. D., of Mass. Terms of Advertising Twenty-five cents per line each insertion. We re-pectfully requent that our patrons will make their advertisements as short as possible. Engravings canEot be admitted into the advertising columns. All advertisements must be paid for before inserting.
This article was originally published with the title "Correspondents"