P. & T., of N. UWe are of opinion that lightning roJs should not be iusulnteu from metallic or -other roofd. If tlie rods uro ia onc piece we do not think that pn.iut destroys their efficiency. If made in scctions, the paint, by becoming interposed bct\veen the jQ.ints, may produce insulation or separation sufficient to cause danger Eo C. H., of N. H. We shall be happy to hear the result of your experiments on hen's eggs, although we cannot scc why eggs laid in August should be better than those laid in any other month. J. H. B., of Ill.A good )Yatcrproof cement is made by disBalving india rubber in coal tar or naphtha. Soda biscuits afC made by substituting carbonate of soua for y east. A. B. K., of C. W.Type metal, consisting of 6 parts of lead und 2 of antimony, or Britannia metal, which is composed of variable quantities of copper, tin, bismuth, and antimony, wonld answer your purpose and take rlding well. J. W., of N. Y.When the atmo,pherc is not fully clmrged with electricity, or in other words;'when the air und earth are not equalized in the qnantity of electricity, it is not in its normal condition, and so will not conduct sound as well as when it is properly charged. But an over-dose of electricity in the atmosphere would be a:) likely to interfere with its somid-conducting pl'OV:l'tics as an under-dose. We do not know of any work treating on this subject; such a book would prove very iuteresting. G. W. C., of N. Y. Haswell is perfectly correct in stating that .tthe centrifugal force of a body making ten nwolutions a minute ia four times as great as when making five revolutions a minute ;1I but you are \Hong in supposing that it only requires twice the power to double the speed, for it takes four times the power to Jouble the speed, so that there is no excess that call be nude available. J. A. L., of Ga.We expect that the reason yoar chimney gctg red hot is, that it is too ncar tho furnace, and your exhaust may cnter the chimney at too highm a point, so that it condenses, and the' air being very rarified indeed where the chimney is hot, the conrlcnsed exhaust steam falls down, cools it, and so produces a dOlvnwurd, instead of an upward draft, for a 8hort timl'. As we do not know all the conditiolls andxcla-tiona of your boller, furnace, engine. and chimney, thin 13 the best theory we can give you. J., of D. C.The reason why the snake-like motion is obacrved in a rope that is agitated in one cnd, is that the material is elastic, und as you disturb the line by moving to one side, there must be a compensating deplrture from the line on the other, and this being conw tinued, the wavy motion is produced, namely, by alternatc compensations, the force applied being quicker than the conducting power of the rope. A. B., of Mass.Evaporated water contains no solid matter, saline air being produced by the air entangling in solid particles of salt which have becn left by the evaporation of sea water. It is a purely mechanical mixture. W. S., of Ind.You had better refer to " The Am-brot.ypc," by Charles Seely, published by Seely & Gar-banati, 424 Broadway, New York. J. T. M., of N. Y.The simplest method we can recommend you for prescrYing egge: is to dip them illsertin grease, and then pack away in oats, or similar material. Yon will find plenty of receipts in back volumes of the SCI. A1. J. 'V., of Uieh.A good clementary work is HUolburn on the Lucomotive," published by Wiley & Halstead of this city. rrhe link-motion id very oldwe think George Stephenson is the inventor. C. C. IL, of IlLA body falls with exactly the game velocity, in the inverse ratio, that it accends, deducting the difference of atmospheric resistance. The law which governs falling bodies is; that the velocity increases ill arithmetical progression, following the odd Dumbers; thus a body failillg sixteen feet the first second, will fall three times sixteen feet the next second, five times sixteen the third second, and so on. D. McGK, of Tcxas.M. & J. H. Buck & Co., of Lebanon, N. H., can furnish you with a brick machine adapted for your purpose. See engraving on page 265. Vol. XI, SCI. Am. J. A., of Pa.If you have a patent on your machine here, a party has no right to make the machine, cven if he does auip it to another country to be used. Your patent protects yon in the sole right to make, sell, use, &c, and a party violating either of theoe conditions is liable to you for infringement. W. D. B., of Mo.We only stated, on the authority of many millers, that water exerts more power at night than in the daytime, and that furnaces draw better at night, "Ve should really like the results of some practical experiments on the subject. Money received at the Scientific American Office on nccouut. of Patent Office business, for the weekending Saturday, July 24,1858 : J. It F., of Ohio, $25; J. C. McD., of Ohio, $60; J. W. C., of Ind., $30; G. M. P., of Mass., $55; S. H., of N. H., $25; F. & B., of Wis., $25; E. D., of La., $30; I P. E., of Ind., $35; J. H. R., of III., $25, E. L., o( Conn., $30; F. McN., of OhIO, $25; J. B., of III., $30; W. B., of N. J., $35; S. N. S., of N. Y., $35: J. W., of N. Y., $25 ; W. P., of Del.. $30; A. W. D., of Me., $30; H. &M.,of Pa., $10; J_ C. DeW., of N. J., $30; J. L., of Mass., $10; C. P. G., o( IlI., $55; P. & D., of N. Y., * $25; B. S. M., of Iowa, $30; A. R., of N. Y., $29; W. M. S.,of -----, $30; W. T. F., of Tenn., $25; J.A., of y Pa., $30; J. D., of N. Y., $27; W. D. A., of N. Y., $55: ft J. R., of N. Y., $57 : W. D., of N. J., $16; B. & R., of M HL, $25; J. A. B., of Ga., $100; W. W. St. C., of VR., |L $27; J. H. B., of N. Y., $35; W. D., of N. J., $14; H. G.,of Ill., $30; J. A. K., of Mo., $55; A. S., of N. Y., $25; M. A. W. of Ohio, $40: J. K., of N. Y., $30; J. A., of-So C., $50; J. J., of N. Y., $20; G. of Conn., $110; R. W., of VI., $25. Specifications and drs wings belonging to parties with the following initiab have been forwarded to tho Patent Office during the week ending Saturday. July 24,1858 : H. & M., of Pa.; J. C. C., of N. Y.; G. W. B., of N. Y.; J. J., of N. Y.; J. H. R, of Ill.; W. B., of N. J.; G. M.t of eonn.; J. A. T., of Ohio; N. T. S., of Mass.; J. D., of N. Y.; F. n. A., of lowa; P. & D., of N. Y.; A_ S., of N. Y.; W. D. A., of N. Y.; J. W., of N_ Y.; G_ M., of Conn. ;B.&R, of Ill.; S. H., of N. H.; E. D., of La.; F. MeN., ot Ohio; A. R., of N. Y.; S. N. S., of N. Y.; R. W.,ofVt. Literary Notices SigneRs oI.' tIle Declaration oF Independence. We have received a copy of a large and handsomely executed chart, containing a history of all the signers of the immortal Declaration. It gives in a brief form the birth place, residence, prQfession, age. number .of children, place of decease, &c. 'rhis is a highly useful and valuable work. It reflects much credit on the author, J. C. Power, of Peoria, Ill. To be had of Duval, rithograpners, Philadelphia or I. S. Clough, 231 Pearl .street, New York. " TIle Country Gentleman entered upon a new volume on the 1st inst. This is a 'Gentleman' that may be taken to your fireside, your parlor or your lib rary with safety. The more familiar ani Intimate your acquaintance, the more your pleaimre and your profit. 'Vo will guarantee its character as above reproach or suspicion. It is one of the very best -of our a.gricultural anu family papers." . rrhe above paragraph from the NC\v York Observer receives our hearty endorsement. TIlE California Culturlst \Vheeler & Wadsworth. publidherH, Sa.n Franciseo.AVe lJave received the first number of this new periodical devoted to agricultnre in California, ann the stndy of nature everywhere. There arc many Buch publicationa in the older States, but for typography, matter and general appearance, ,butthis equal a any one of them, and it ia in every way a credit t2 the Golden State. TUe ScalpelE. H. Dixon, M. D., Editor, and published by Sherman & Co., No. 1 Vesey street, New York.This valuable publication, which has an honest abhorrence of humbug, Whether professional or not, is the ablest journal of its kind this side the Atlantic, or rather we should not say hof its kind," for it is distinctive and stands alone an open, honcst oasis in a Lroad desert of medica.l quackery, interesting aa a romancc, and truthful as hbtory. 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