J. F. R., of Pa.—The machine for urilling the Hoosac tunnel is driven by a steam engine. A number of drills are oper.”ateu at once ; these receive a motion on theiI vertical axes as thay nre struck by the h,ltnmcrs. You willfinda drilling machine illustrated on page 153, Vol. III. (old series) of the SCIENTIFIC AMEB-LOAN. D. Ho, of N. C.—ICarbon oil,.”so calleu here, is not mnde from rosin tar, we believe. bllt from coal. The way to burn rosin tnr. to obtain lampblack, jg to place it in n furnace and burn it with a emtdl nmount of ail"^ conducting the stnoke into cylindrical chambers hung with coarse bags, upon the surface of which the lampblack is depo3ited. J. P. S., of Ky.—A magnetic, locomotive driving 1vheel wOllhl not bB patentable in itgelf. hnt there may be some featut'e of B patentable character in the details of its constl'lIction When you send the model wc shall be able to give a more definite [ opinion. Superheated steam can be used expansively ivith ns much advantl\ge as saturated steam, so far as we can judge flom the stntcments of those who have thus employed it. D. C., of N. Y.—Thcre is nothing pntentable ahout the sulphur vapor bath, as far as we havc becn able to ascertain. A. W.( of Conn.—You will find a full illustrated description of the processes and compositions for enameling iron oa page 182, Vol. IX. (old series), of the SMENTIFIO AMERICAN. It would take up too much of onr time to describe t',1e processes by letter. L. K. W., of Va.—The SCN:NTIFIC AMERICAN is the only source wherc you can obtain iuformation respecting the general progress of invention 10r the past 15 yenrs. You wIll find an electric lamp illustrated on p as e 404, Vol. VIII. (old eeries). T. II., of Mo.—As we understand your questIOn, it will take thesame amount of power to drhc a pinion placed at any part of the inside rim of a large sjnir wheel rolling on the ground. To balance the resistance to the large wheel, however, it would be thc mos't suitable position to act the pitlion directly in lille ' above the point of contact, where the wheel touches the ground. J. B. S., of 'Vis.—In launuries, mangles are employeu for pressing sheets and other kinds of domestic linen. The fine gloss is put up:m collara nnd bosoms with the iron rubbed on rapidly while hot. The collars are l)lnced on a hard surf ace of pasteboard, and they require a Rood 1)Qdy of stnrch containing a minute qnantity of sperm. S. C., of Va.—The neeule will dip in proportion to its nearness to the magnetic poles. A due llortll line is not that of the mnximulll dip of the needle at present. The magnetic pole Is at a point about 10 from the north pole. By changing the magnetic mel'idi,\n east or west, the dip of the needle varies accordingly, and it is crmtinually changing. The magnetic poles seem to have a slow revolution round the trne poles of t11e earth. W. R A., of Penn.—A hO"se-power is power sufficient torais 33,000 Ib3. oue foot high in one minute. A column of I water. 20 inches in diameter and 56 feet long, contains 122.17 cubic feet, and weighs, at 63Jtf lba. to the cnbic foot, 7,665 Ibs. To raise this weIght 240 feet requires 1,839,600 foot pounds, nnd to accom. pllsh thig work during each minute would require 55 4-5 horse power. A sinale aetine ?s??. wit.h R yinder 38 inches in diam. ~ . ?* u leet troke, making 20 Idrokes per mirrate, with eteam t 100 lbs. pressure, would give a gross yield of 550 horse-power deducting J for friction, Sus^ and we haVe a net power ot 413 horses. W. P. H., of III.— Yolll method of supplying a con ttnuoui airema of merowy to Way1 eleetrle light U Lngeotoui ad we believe it u also pMenuUe . ?, M., of C. W.—You can purchase the colors for graining oak at any good paint store. These colors are made of ipnna, umber nnd Vandyke -brown. They nre put on a lighter ground, and the streaks nod wave line's nre made by removing portions of the conting with a piece of soft leather or rags placed upon the nrtiEt's finger. A woolen comb is cmploypd to make the fine streaks or grain?. It requires much skill nnd good taste to be a first rate srainer of wood. J. P., of Aln.—An exccllent cement for slabs of marble is mnde by steeping plaster of Paris in a strong solution of alum then drying nod calcining it, after which it h reduced to puwder and is fit for use by mixing with water. This cement becomcs vcry hard, but is not adapted for exposure to the wcather. It is useful for setting the tiles and slabs of tcsselated pavements, nnd may be employed as a substitute for etucco in making plastcr ornaments. 'Ve cannot sive rou the information Fcqucstcd about the nitrate of thc oxyd of glyccrine. J. G., of C. W.—The cost for an English pntent is the same to a British subject as to nllY American citizen. A good metal for making models U 20 ounces copper to 10 of tin. It is sufficiently tOllsh nnd is cnsily worked. It is necessary to put rollers in rour model and render every part completc on which any claim is tobe based. J. M. G., of N. ?—Though tllere is great difference of opinion about the time of tkc first olympiad, chronologera agree to reckon from tke one the first year of which Mas the 776th before Christ. Consequently, thia is 'the 659th, as you say. As Protestor Pierce, of Cambridge. is interested in the U American Nautical Almanac,1I if you will write to him, he will inform you where you can procure it. C. A. B., of N. Y.—Benzole is to be had in this city at $1.25 pcr gallon. G. D. G., of N. Y.—The alloy of all the United States silver coins consists of nine parts of silver to one of base metal. The weight of the three ceut piece is 11 52-100 grains. C. W. B., of N. Y.—The statement that a caloric engine could be run with au expenditure of n half llOund of coal per horse-power pel' hour ,vas probably intended to be under8tood as theoretical. 'Ve do not believe that this has ever been realised. W. 'V., of Ind.—As the axle ot the gyrascope is supported at one end, the revolving disk at the opposite end cannot fall wIthout changing the plane of its rotation; but as gravity overcomes the resistance offered by the inertia of the rotating rfiskto this change of plrme, the effort to preserve the same plane of rotation causes the revolution around the center. S. D. S., of Tenn.—You will find articles on the re-farming of our weightR and measures on pages 54 and 70 of the pt'eseut volume of thc SCIENTIFLO AMEBICAN. D. W., of IlI.—'Ve do not know anything better to prevent polished iros work from rusting and turning black than common c1enr varnish, containing a little bleached becswax. Clear copal varnish is ycry good of itself for t11e purpose, because it contains linseed oil. J. M. L., of Mich.—Tha pnper for Bains' chemical telegraph was preparcd with the prussiate of potash and a small quantity of the chloride of calcium. The latter kept the paper in moist condition. Y{c are not ncquninted with any gooe\ reason why the chemical telcgraph wns abandoned. Yon will find the best modes of constructing batteries described in Prescott's able work on the telcgraph. S. R. K., of Mich.—The following is a simple rule to ascertain the nominal horse-power of ng common condensing engine:—H Uultiply the eqnare of the diameter of the c}'liuder in inches l)y thecubcroot of thc Etl'oke in feet, nnd dividethe product by 47; the qlloticnt is the number of nominal horaee-power of the engine..”This rille assume8 the existence of a uniform effective pressnre upon the piston or.”7 lbs. per sqnare iuch, The actual power of an engine can only be ascertained bv the usc of an indicntm attached to the cylinder, to indicate the amount of pres. sure or V1\CI:um existing within the cylinder. About one ponnd nnd a half of the pressure per square inch is “Uowell for friction, working the air pump, &c.\ expended on the eosine itself.I F