J. H. C, of Pa—Your communication lias been received, and will be titU'iidi d to next week. C. B.,of Mass.—We arc not acquainted with the gaa apparatus referred to in the extract you have sent us. Probably it is simil ir to the portable rosin oil gas generators, some of which are very excellent for small factories and public buildings. Illuminating gas can be made from any refuse grease, in a common retort, just as well as the one mentioned in the extract. S. F. C, of La.—Pewter is very malleable and ductile; it is composed of 80 parts of tin and 20 of lead by weight, fused together with frequent stirring. B. J., of Mo.—The micrometer is a small instrument adapted to a telescope for the purpose of measuring short distances, or the diameters of objects which subtend very small angles, as those of the heavenly bodies. Its name is derived from two Greek words signifying a small measurer. W. II. D. C, of N. H.— An excellent place for you to receive a thorough training in civil engineering, would be at Union College, Schenectady, N. Y. Professor Gillespie's works on Surveying and Roadmaking are good. Professor Mahan on Civil Engineering is also an excellent work. M. M. H. C. W., of C. W.— You will find the alloy you mention on page 76 of the present volume, and you must have confounded it with an article on silicum oa page M. By referring to them both you mil discover all you wish to know. W. S. II., of Ct.—We do not know anything about the patent to which you refer. All patented machines must be so stamped. If tb:a is not done, the inference is strong that no patent has ever l;er-n granted. J. T. McG., of Md—Acids are not einv!o0-l fur polishing the barrels ofrilles. Emory and oil aiv I'sed for this purpose, and they are iini.-ht-d hy the u1 of a burnisher or polishing tool. J. D. B. of Ala.—The two wings oJf the new eapitol ai Washington are not, as we under, land it, oi precisely the same order of architecture as the old building, but there is a tolerable unity of design preserved in the addition. We have not at hand just the information you want on this subject, but no doubt at the proper time a full account of the buildings will be published. H. A., of Ohio.—The mode of setting eccentrics depends much upon the form of the valve, and whether you want any lead. If the valve has no lap, and no lead is desired, the eccentric should be at right angles to the cranks of their respective cylinders, and the valves will then commence opening the steam ports as the cranks pass the center. A little lead is, however, desirable, and this requires the eccentrics to be set a little in advance of the above mentioned position. You had better consult come good work on the steam engine, as this is one of the most important parts of the engine. The Artisan Treatise, by .John Bourne, is a very good work. M. M., of Wis.—We are prepared to push forward your application for a patent on the shingle machine improvement with vigor as soon as we receive the model. The business of the Patent Office is going on with accumulated energy under the new Commissioner, and we think inventors generally will have no occasion to complain of its management. II. G. F., of 111.—We have been assured by a practical plasterer and builder that plaster dried rapidly and thoroughly by freezing makes as good walls as that dried during warm weather. We have never tried, the experiment ourselves, but would prefer walls plastered in summer to those so treated during frosty weather. H. C, of Ohio.—We cannot encourage you to spend money on an application for a patent on your alleged improvement in barrel machinery. The combination of the catting head with the shifting gear is not new. The preliminary examination shows valid references against your claim, and we cannot expect to succeed where there is so slight a chance to found a claim. We thank you for the generous list of subscribers. Send in all the names you can procure before the 1st of January? at which time we shall publish the award of our prizes- W. P., of Ey.—In some parts of the world where steam power is not much used, and large pumps but little known, it is common to use an Archimedes screw for elevating water. It was first used by the philosopher whose name it bears, for raising water and draining land in Egypt. It consists of a large tube coiled round a shaft of wood to keep it in place and give it support. Both ends of the tube are open, the lower one dipping into the water to be raised, and the upper one on the machine being turned, pours out an intermitting stream. The shaft turns on a support at each end, the upper support being elevated in the air, and the lower o.ae i.-* immersed in the ater. E. C. M.,of N. B.—Your idea of a thormoinetfr is.* quite an old one. What is known as the pyrometer, which is a thermometer for very high temperatures, is on this principle. W. W. S., of N. Y.—Without suitable engravings it would be impossible for us to furnish an intelligible description of the machinery used in the manufacture of envelopes. You can address Robert MeNie, 39 Greene street, this city, who manufactures the most improved machines for cutting envelopes. J. H. J., of Texas.—We cannot offer you the slightest encouragement to attempt to procure a patent on your rotary engine. It does not contain novelty sufficien t to justify an application, besides, we do not discover any useful feature in the arrangement. J. H. S., of Ind.—It would be very desirable to have some apparatus whereby the vigilance of night-watchmen could be ascertained; and we have often wondered why some ingenious inventor has not set his wits at work to produce it. There is nothing known to us for 1 this purpose, except the well known " tell-tale clock." J. C, of Ind.—We do not know where you can pur- chase one oi" Baker's patent mangloe. We presume lowever, thai-, J. & C. Berrien, of this city, can supply me, but not the gearing apart from tho complete ma-;hiae. A. IT.. of Ky.—We are not aware of any existing influence at Washington against the i?sue of a patent for your improvement. Borne one lias started this report, ao doubt, with a view to alarm you. No such influence is you speak of could have the slightest weight with the Commissioner; and we can assure you that your interests in our hands will be faithfully guarded. C. M., of Mass.—No amalgamation can take place between the copper and iron by Oudry's system of coppering or electro-plating, because there is a coating of var-uish interposed between them. The process is one of common electro-plating, and is described in every work on that subject. If, instead of using a bag, you had employed porous earthenware vessels, you would have been quite successful. J. S., of C. W.—We perfectly appreciate your complaint that books on botany and science generally use hard and technical words, without deigning to explain them. We earnestly wish a reform could take place in scientific literature; until it does, however, we shall be happy to be able to act as interpreters to our enterprising correspondents, who have to light with many difficulties ere they can pluck a single blossom from the tree of knowledge. The vascular tissue of plants consist of simple membraneous tubes, tapering lo each end, but often ending abruptly, either having a iibor generated spirally on the inside, or having their walk marked by transverse bars, arranged more, or IOFS in a spiral direction. There are two principal kinds of vascular tissue, viz,, spiral vessc-K and ducts, or lenders. The former present the continuous spiral fiber, and are capable of unrolling with elasticity ; the latter present transverse line;., rings, or Lar;!, nnd arc incapable of unrolling without breaking. J. II. B., of Ind.—The term or prefix sssqnl in chemistry is ait abbreviation from the Latin word semisqi'e, signifying "and a half.1' It is used to denote one "body combining with another body not in equivalent proportions, but in tho proportion of one to one and a-half; it K however, usual to state such a combination as two to three; as, sesquioxyd of iron—meaning two equivalents of iron combined with three of oxygen; n!?o sesqui-carbonate of alumina—iignifying two equivalents of alumina to three of carbonic acid; and the same in many similar case?. L. A. J., ot Va.—In geology the word " rodk" denoted the solid partrf of tho crust of the earth, composed of a single mineral species, or two or more species. One or several rocks united by certain common characters, constitute a " formation," or connected series, and several formations constitute a system of rocks. Rocks have been distinguished, according to ther physical peculiarities, into the Plutonic, the aqueous, and the volcanic rocks. K J., of Mich. —Corundum is a stone found in India and China ; it crystalizes ia six-sided prisms, and has, from its hardness, been called adamantine spar. The amethyst, ruby, sapphire, and topaz are considered varieties of this spar, differing chiefly in color. These are termed Oriental gc-ms; but the same names are applied to stones from other countries. Money received at the Scientific American Office on account of Patent Oiiice business, for the week ending Saturday, November 2*, 1857 :— II. B., of N. Y., $383 23 ; W. M., of Ky., $5 ; li. & II., of 111., $23; H. T. S., of ft. r.,$25; I). G-., of Pa., $15 ; F. L. W., of S. C, $30; J. V. J., of Mich., $25; E. W., of Pa., $55 ; ,7. E. II., of N. Y., $25 ; V. It. D., of 111., $30 ; 1). l'l, of Ohio, $25. Literary Notices EMERSON'S MAGAZIMS AND PCTXAAL'B MONTHLY fr Peeember, contains a great variety of good and interesting matter, such as cannot but afford tho reader a fund of information and amusement. The article on American Contributions to Science is ably written, and has evidently been compiled by one well acquainted with his subject. This magazine has decidedly improved in tone and character since the two above have become one. BKALSTON'S HANDBOOK OF PRACTICAL RECEIPTS.— Lindsay & Blakiston, Philadelphia. A mos* useful book, full of condensed information on just those subjects which every one wants to know, as it tells you what the majority of compounds are, and how to make them. THE EDIXBUSGH REVIEW—Leonard Scott & Co., New York—for this month, has in it an excellent article on Napierand another on India, besides reviews and essays of and on various subjects. It is a most interesting number. To Our Subscribers RECEIPTS—When money is paid at the office for subscription, a receipt for it will always be given; but when subscribers remit their money by mail, they may consider the arrival of the first paper a bonajlde acknowledgment of the receipt of their funds. The Post Office law does not allow publishers to enclose receipts in the paper. Terms of Advertising Twenty-live cents per line each insertion. "We respectfully request that our patrons will make their advertisements as short as possible. Engravings cannot be admitted into the advertising columns. %* All advertisements must be paid for before inserting.
This article was originally published with the title "Correspondents" in Scientific American 13, 13, 103 (December 1857)