In the road cut by Napoleon between Savoy and France, and about two miles from Les Echelles, there is a gallery twenty-seven feet high and broad, and nine hundred and sixty feet in length, formed in the solid rock. When this road was nearly complete, and the excavations commenced at each end almost met, the partition was broken through by a pick-axe, and a loud and deep sound was heard. We are indebted to Mr. Bakewell for the following solution of this phenomenon. The mountain rises full one thousand feet above the passage, and fifteen hundred above the valley. The air, on the eastern side of the mountain, is sheltered both on the south and west from the sun’s rays; and consequently must be much colder than on the western side. The mountain, therefore, formed a partition between the hot air of the valley, and the cold air of the ravines on the eastern side. When the opening was made, the cold, and therefore denser air, rushed into that rarefied by heat, and a loud report was produced, in the same manner as when a bladder, placed over an exhausted air-pump receiver, is burst. Baron Humboldt informs us, on credible authority, that subterranean sounds, resembling the tones of an organ, are heard on the banks of the Oroonoko. He supposes that they arise from a difference of temperature between the external atmosphere and the air confined in the crevices of the adjacent granitic rocks. He concludes that, as the temperature of the confined air is greatly increased during the day from the conduction of heat by the rocks; and as the difference of temperature between it and the atmosphere will reach its maximum about sunrise, the sounds are produced by the escaping current. The following illustrative experiment is not a little curious:--If a tube formed of some elastic and sonorous substance be taken, and a jet of inflamed hydrogen be introduced, a musical sound will be heard. This will take place in a tube closed at one end, if it be large enough to admit a sufficient quantity of atmospheric air to support the combustion of the gas; but if the tube be open at both extremities, the musical sound will be clear and full. Various conclusions have been arrived at in reference to this phenomenon; but they have been set aside by the experiments of Mr. Faraday, who attributes the sounds produced by flames in tubes to a continual series of detonations or explosions. The first philosopher who exhibited the longitudinal vibration of solids was Dr. Chladni. According to him, the best method of producing these vibrations in rods, is by rubbing them, in the direction of their length, with some soft substance, covered with powdered resin, or by the finger. When glass tubes are employed, they should be rubbed with a piece of rag spread over with fine sand, the tube being held by one of the ends.