CORRESPONDENTS who expect to receive answers to their letters must. in all cases, sign their names. We have a right to know those who seek information from us; beside, as sometimes happens, we may prefer to address correspondents by mail. SPECIAL NOTE.-This column is designed for the general interest and instruction of our readers,notforgratuitous rep lies'to questions of a purely business or personal nature. We will publish such inquiries, Aoweyer, luhen paid for a8 advertisernets at $1'00 a line, under tke head of “Business and Personal." All reference to back numbers should be by volume and page. J. D. P., 0f N. Y.The broad gage railways are failures only because they are, for various reasons, so expensive in their °perat;ion' We can not enter at this time into a detailed account of these causes They are good for th? passengers but hard on the companies who °wn them. M. G., 0f Minn.Your sketch is very imperfect, but from what we can understand of it, it shows no patentable improvement. It wot^ therefore, be scarcely worth while to enter into the computation necessary to determine what strain such a structure would sustain. S. E. W., 0f N. Y.-Friction would be reduced in using friction rollers under your shaft in proportion to the diminished surfaces of the journals. The size must depend upon the circumstances of the case. Make the rollers as large as you can conveniently . C. T. G., of Pa.It would be impossible to give you tbe . knoWledge you require in the form of a recipe. A small volume caiied “The Complete Practical Brewer,” published by Henry Carey Baird, of Philadelphia, gives the precise information you require. J. M. H., of Wis.We know of no steam apparatus which Wfll meet your requirements and Which you can purchase ready mnde You might, it seems to us, easily devise one for yourself. Set your Wits t work. It. S. B., of Ky.The minerals you send appear to contain ir0n and perhaps copper, with sulphur and arsenic. We cannot determine Whether other metals of value are present without making an assay. M. S. M., of Mo.The stones you send are agate and ehalce- dony. They have little value except When worked and polished. They are rendered valuable according' the labor bestowed upon them. E. H. S., of N. H.You will find an article fully treating your question about long and short screw drivers in the Sciektifk American, Vol. XVIII, No, 25, page 393, June 20, 1868. mmm gatms. Issued by the United States Patent Office. FOR THE WEEK ENDING OCT. 5, 1869. Reported Officially for the Scientific American !!ISCHEDULE OF PATENT OFFICE FEES: On eacn caveat$10 On filing each application for a Patent (seventeen years)$15 On issuing each original Patent$20 On appeal to Commissioner of Patents$20 On application for Reissue$30 On application for Extension of Patent.$,50 On granting the Extension$50 On filing aDisclaimer$10 On a 1 application for Design (three and a half years)fio On an application for Design (seven years)$1 j On an application for Design (fourteen years)$30 In addition to which there are some small revenue-stamp taxes. Resident s ot Canada and Nova Scotia pay $500 on application. For copy of Claim of any Patent issued within 30 years$1 A sketch from the model or drawnig, relating to such portion 0/ a machine as the Claim covers,from$1 upward, but usually at the price above-named. ThefuU Specification of any patent issued since Nov. 20, 1866, at tvhich time the Patent Office commenced printing them$1*25 Official Copies 0 Drawingsof any patent issued since 1836, we can supply at a reasonable cost,the price depending upon the amount 12^ labor involvedand the number ofviews. Pnll Onformation, as to price QI drawings, in each case, may be had by address ingllIUNN&CO., Patent Solicitor's, No. 37 Parle Row, New York. gutfttiAS and ^wmmt The Charge for Insertion underthis head is One Dollar a Line. If the -Notices exceed Four Lines, One Dollar and a Half per line will be charge. A.H. B., of Pa.A body floating in a fluid medium, and sustaining by its buoyancy just as much weight as it is capable of supporting, would descend through that medium by the addition of just sufficient weight to overcome the friction of the fluid against its sides, It will then certainly take as much (practically more) weight to draw it down through thatfluid as it can raise by its buoyancy. In the answer to the correspondent about the balloon, the endeavor was to make this point clear, and to show that a balloon in rising could exert no more force (practically not so much) than would be required to pull it down again. W. A. H., of Tenn.The plan of closing a well air tight at its mouth and inserting, a pipe to reach below the surface of the contained water, and raising the water by forcing air into the well Will Work in some cases, but it is neither new, patentable, nor practicable. Because the top of a Wheel rolling along a level surface moves faster ahead relatively to any point on that surface than the bottom, it does not follow that its circumferential motion is greater at the top than at the bottom. What we mean by circumferential motion, is the motion of all points in the circumference around the axis of the Wheel. J. A., of Ill.The photographer has the best of it. The contraction of the pupil of the eye does not diminish the apparent size of external objects. The reason of the apparently larger size of the sun and moon When near the horizon is probably that they are then in immediate contrast With terrestrial objects, by Which their size is estimated, While in the zenith no such standard of comparison can be simultaneously viewed With them. B.J. J., of Va.We would not recommend the arrangement of piping for a lumber drying-house you propose. “A Practical Treatise on Heat,” published by Henry Carey Baird, of Philadelphia, Will instruct you properly on this subject. There ought to be good ventilation in any room used for drying purposes. Your last question cannot be answered in the form you put it. J. B. W., of Pa.Your suggestions for ventilating mines by forcing air down through a main pipe by steam power, and delivering it through branch pipes, contain nothing new. This is, however, a good plan, and it, or its equivalent, has been tried successfully in English coal mines. We agree with you that either this or some other equally effective system ought to be generally adopted in working coal mines. J. W. P., of Me.The best material for a step to a turbine Wheel is probably lignum vital. That your steps burn out indicates that the Wheel is not balanced properly to take off its weight from the step. If it is not practicable to balance it in this way your only remedy Will be to increase the size ofthe bearing in proportion to the weight of the wheel. G. M. S., of Miss.The power oi an engine having a twenty- inch stroke would be to one having a thirty-inch stroke, everything else being equal and the steam being worked non-expansively, as one to two. This, of course, supposes everything so arranged that the mean effective pressure in the cylinders should be the same throughout their respective strokes. F. C. B., of Ohio.To scale sheet steel, use a wooden trough lined with sheet lead. Use crude sulphuric acid, 0ne part of acid to ten of water, by measure, or rather more dilute, let the sheets remain only a very short time in the bath, take them out and wash t1em in hot lime water, and then rub them With clean dry saw dust or chaff. W. Z., of La.The appearance of gold, copper, or brass, is given to tin plate by the application of suitable lackers. You can purchase these lackers at dealers in varnishes, etc. F.D. H., of N. Y.You can dissolve rubber in naphtha to a thick solution and With It stop small holes in rubber. Apply it soft and allow it to harden thoroughly. G.G. B., of N. H.The mineral specimen seems a schist eon- taining iron. It appears to be of no value, but analysis might .give a different rssul t. Send for Agents' Circular-Hinkley Knitting Machine Co., 176 Broadway.