CORRESPONDESTS wko expect Pa rescue anitmers to their Utta-emust, m aUaues,stm tlutrname*, W kam a rtQht to knms tM( who teeltin-fotrmaUtmrramm; itesMe,weotruifmm happens, we may pnf'f to as. dress oorrespm-tdenuov meUi. SPECIAL NOT S.-This eotanwtoNrtSiSMi for the mural mttrett am* Instruction of our rtadtrt, tun forjraiuttom rtptta to quUmu off purely buxtnaaw vtrmnut nature. Ws will publish mtch twjufrtm, Aowem-kAm paM fbr at mdt*rttotmtt at vi-do a Mm, umUr tk* hml of "Smut. nsasand ftfBMI." %WAlI YZf efmcs so hock. numbers shutd be by volume sndpugs* C. H. S, of Pa.A pendulum tliAt vibrates seconds in tie latitude of New York city. Is according to Sa-Ker, SMM8T48 tnebes to leugtb, from the point or suspension to the center of oscillation. This length, or tlie known lengths of pendulums, beating seconds at. other points would form a bsslsfor tlie restoration of tSje standard foot should It ever become lost. It Is probable, however, tliat the foot will before manj yews 80 act of tisc as a unit of meiBOTemeot, and the meter become universally oaed instead. F. It.,of X. Y.The advantage gained by condensation in steam engine*, I* not as manj ontbeoretlcal mess suppose , owing to the sccuieulsitlon of pressure on %w glde of the piston where the etesm Is act. Sag upon It, but to tbe removal of the retlstace of the pressure of the atmosphere upon the cxhaoat. Tlilt res'stancc can nerer be more than fifteen ponnds.In round numbers, A meronrlai eoinmoiiiocbea In hlKtrt, balsoeos sbeot 1? lba. atmosphcrle pressure to the s4nare Ineh, eabjeet to some reflation* Tor different altitudes, teniperstnrcs, etc. F. O. N., of Mass.A good cement for uniting iron pipes that will withstand the action of not water to made by mixing clean Iron nl-Ibss, or podercd Ijorlojs, with powdered sal ammoslacand eulplinr: 1 part by wislghtof sulphur, 3 of sl ammonlae, and SOo/lron. After mlx-lg,sUt coarsely mnd mix with water as It la used, to small tnauhUee a t a time, B. P. P., of Miss.Either the screw, or wheel and axle, of which gearing is & modSScatSoo, have a power wbScli le limited only hj" Btrynili of muterlMs. Aglvoo power will however rslae more weight So s lvcss tlmeb ya eomblaaUou Clearing'thaehj" as,row,as tketstterab, serne more of the power by lrletlon. T. H. M., of N. T.If you intend to invent a machine for set- tlngand distributing type,you most famlllsrlssyourse f by personal e%-amlnatloa, with the practical details of thebUBlnfes. J. J. B.i of Ohio.To obtain an engineer's certificate.yoa mast possess & practical koowlede of the eongS-ract on sod operation of tbe steam engine. H. F. U., of Pa.-Lime washes may he tinted with ochers, or other earthy plgmenle, Iheawonnt of wblch is rculatKd bj the deptb of tint required- The addition of aemsll quantity of gloe asd eulpbate of zinc, will give greater permanency to tbe eoatlag than It wonld possess wiWtootit. A little experiment will enable yon to Hi upon tbe right Proportions. J. W., of Ohio.Ono equivalent of chlorine, and one equivalent of hydrogen form hydroeblorlc add, bo matter what means re e ployed toeS'ectt lie combluatloe. J. A. P., of N. Y.We should use brass to make the toy wheel or which you Bpesk, mating the step of soft metal and the Bhaftof bud metal. S. W. W., of Mass., wishes to know of a prosess by which oil can be extracted from leather without lojury to the leather;perhaps eome of our eorrespondente may know ol Bueba process. J, E.G., of Pa.A complete answer to your (inquiry may be foundnpage39S,Yot.XYIIt,of the Scixxtifio Axkstcax. Mechanical Engravings Sftchas emhelllsh tlie Sciswiino Abiiicu*, are genefally snperlor to those of any simitar publlestlon. either In thin coaotry or In Europe. T ey are prepared b jonrown srttots.who have tod lonjeiperience In this branch of artauedwbo work eicleslvelj-for ns. There Is one pertlocnt fact In eouaectlon with the preparation and publication of an Illustration tn onr columns, that needs to he better anderatood by many inTentore and mno-ractnrers who perenc gMort.alghted.pciUcy In brlnglau their Improvement* to pnbSle notice. Thefoften gotoa large expense in printing aod circs-Istlng handbills, whleb few care either to read or preserve. Now, we undertake to eay, tb She cost of a Srst-claegeaigirsvltisr, done byoarowp artlsls, and printed la one tssne of the Soieht'Itic Asshioak, will emomnt to less tbaii oae.hsir tbe wn tba wonldbave to be expended 0 d a poorer Ulnatra-tlon. printed In tbe tine number of clreDlare,and o 6 a sheet of paper tn elzs ecinal to ooe page of rar journal. A printed handbill has do permauenl Talse. Thousands of TOlmmet of the Scibhtijio Ambeicah ore bound and preserved for fsture refereaeebeside* we estimate that every ISine of our pper te read by no fewer than one hundred thousand persona. Partlee who desire to haye tlielr loTentlons IBoetreted can address the nnderslgscd.s'ho are also prepared to send srtlslg to make sketebee of mannf actBrS?i et@-l-liatimeotti with a view to their publication In Ibe BetKB amrbicajj. For particulars address MUN 4 CO., 87 YsrK Bow, Hew York