A. The ear is fitted with a small membrane called _the drum_ (or tympanum), through which the dense air bursts, and the rupture very often _produces incurable deafness_. Q. _Why do our CORNS ache just previous to RAIN?_ A. Previous to rain, the density of air is greatly lowered (as every one knows from the fall of the barometer); in consequence of an unequal pressure, _our feet swell_; but the hard corn, _not being elastic_, is painfully stretched and pressed. (Some of this pain is due to electricity.) Q. _Why do CELLARS feel WARM in WINTER?_ A. As the external air has not free access into cellars, they remain at a _pretty even temperature_, which (in winter time) is about 10 degrees _warmer_ than the external air. Q. _Why do CELLARS feel COLD in SUMMER time?_ A. As the external air has not free access into cellars, they remain at a _pretty even temperature_, which (in summer time) is about 10 degrees _colder_ than the external air. Q. _Why does lightning strike the OAK-tree more frequently than any OTHER tree?_ A. 1st--Because the _grain of the oak, being closer_ than that of any other tree, renders it a better conductor: and 2ndly--The _sap_ of the oak contains a _large quantity of iron_ in solution, which is a most admirable conductor of lightning. Q. _Why does AIR rust IRON?_ A. The _oxygen of the air_ combines with the _surface of the iron_, and produces _oxide of iron_, which is generally called rust. This rust is a species of combustion. Q. _Why does hot iron SCALE and PEEL off, when struck with a HAMMER?_ A. The _oxygen of the air_ very readily unites with _the surface of the hot iron_, and forms a metallic oxide (or rust) which scales off when struck with a hammer. Q. _Does iron RUST in DRY air?_ A. No; iron undergoes no change in dry air. Q. _Why do STOVES and FIRE-IRONS become RUSTY, in rooms which are not OCCUPIED?_ A. Because the air is damp; and moist air _oxidizes_ (or rusts) iron and steel. Q. _In what part of the year is it most difficult to keep STOVES and FIRE-IRONS BRIGHT?_ A. In _autumn and winter_; because the capacity of the air for holding water _being on the decrease_, its vapour is deposited on every-thing with which it comes in contact. Q. _Why does GREASING iron prevent its becoming RUSTY?_ A. Because _grease_ prevents the humidity of air from coming in contact with the _surface of the iron_. Q. _Why do not STOVES rust so frequently as POKERS and TONGS?_ A. Because stoves are generally _covered with plumbago_, or black lead. Q. _What is plumbago, or black lead?_ A. A mixture of charcoal and iron filings. A most excellent varnish to prevent rust is made of 1 pint of fat oil varnish, mixed with 5 pints of highly rectified spirits of turpentine, rubbed on the iron or steel with a piece of sponge. This varnish may be applied to bright stoves and even mathematical instruments, without injuring their delicate polish.