in such a manner that the solution as formed may drain off. Such a battery continues in action as long as the air contains moisture; the only means of stopping it is to shut it up in an air-tight case. The electro-motive force depends on the degree of humidity in the air, and also upon the temperature. * * * * * ANALYSIS OF PERFUMED SCOURING PASTES.--The analysis of No. 1 resulted in water and traces of myrbane oil, 3.66 per cent.; fatty acid, melting at 104° F., 54.18 per cent.; iron peroxide, 10.11 per cent.; silicic acid, 14.48 per cent.; alumina, 17.31 per cent.; lime and magnesia, traces. The iron peroxide is partly soluble in hydrochloric acid, the alumina entirely so as silicate. The scouring paste, therefore, is composed of 54 per cent. fatty (palm oil) acid, 10 per cent. jeweler's rouge, 32 per cent. pumice-stone powder. * * * * * SOUND SIGNALS. In Appleton's "Annual Cyclopædia" for 1883, Mr. Arnold B. Johnson, Chief Clerk of the Lighthouse Board, contributes a mass of very interesting information, under the above title. His descriptions of the most approved inventions relating thereto are interesting, and we make the following extracts: The sound signals generally used to guide mariners, especially during fogs, are, with certain modifications, sirens, trumpets, steam-whistles, bell-boats, bell-buoys, whistling buoys, bells struck by machinery, cannons fired by powder or gun cotton, rockets, and gongs. _Gongs._--Gongs are somewhat used on lightships, especially in British waters. They are intended for use at close quarters. Leonce Reynaud, of the French lighthouse service, has given their mean effective range as barely 550 yards. They are of most use in harbors, short channels, and like places, where a long range would be unnecessary. They have been used but little in United States waters. The term "effective range" is used here to signify the actual distance at which, under the most unfavorable circumstances, a signal can generally be heard on board of a paddle-wheel steamer in a heavy sea-way.