A.K.S., of Ohio.--The inclination of the poles of a planet to the plane of its orbit, determines its zones and also its seasons. The inclination of the earth's axis is twenty-three and one half degrees. This places the tropics the same distance each side of the equator, and the polar circles the same distance from the poles. The torrid zone is therefore forty-seven degrees wide, and the temperate zones each forty-three degrees wide. As the planets vary in their inclination of their axis to the planes of their orbits, it follows that their zones and seasons differ from those of the earth. W.H.C., of Texas.--The teeth of a circular wood saw to be driven by foot-power, should be not larger than those of the ordinary hand crosscut. The fly-wheel ought to have a rim weighing from eighty to one hundred pounds, and it should be, for a 12-inch saw, not less than a foot in diameter. It should be placed on the saw arbor. The belt should not run on the fly-wheel, but on a special pulley, and the treadle and crank motion should be so adjusted that the foot will move through an arc of from 10 to 12 inches. A.H.B., of Pa.--We advise you to use a battery in coating the small gray castings, of which you write, with copper. It will be all the more satisfactory in the end. The best polishing material to put in with them in the tumbler we think would be leather cuttings and sweepings. They will not need returning to the tumbler after being coppered. We recommend you to get "Byrne's Practical Metalworkers Assistant," published by Henry Carey Baird, Philadelphia. J.H.G., of Tenn.--Don't put oil in your boiler to prevent incrustation. It will not probably do any good, and it will cause much foaming, while besides that it is a waste of heat, it is injurious to engines. S.S.R., of Tenn.--No ammoniacal engines are, so far as we are aware, running in this country. C.E.C., of Ohio.--The varnish for patterns is common shellac varnish. It is sometimes made black by lampblack. * * * * * RECENT AMERICAN AND FOREIGN PATENTS. _Under this heading we shall publish weekly notes of some of the more prominent home and foreign patents_. * * * * * MOP.--Philip Cook, Jr., Sioux City, Iowa.--This invention relates to a new and useful improvement in mops, whereby they are so arranged that they may be wrung or freed from water when in use by moving the slides connected with the handle and head of the mop. VENTILATING HORSE COVER.--Charles P. Eager, Boston., Mass.--This invention relates to a new horse cover, which is so arranged that it will be entirely waterproof, and nevertheless permit a free escape of air from the body of the animal. CAR COUPLING.--S.O. Campbell, Tipton, Mo.--This invention relates to a new car coupling, which is so arranged that it will be self-coupling and retain the coupling pin ready to lock as long as the link is not inserted.