. Annual report of the Board of Regents of the Smithsonian Institution. Smithsonian Institution; Smithsonian Institution. Archives; Discoveries in science. PRINCIPLES OF THE JIECIIANICAL THEORY OF HEAT. 271. •which is wrapped around with wire and provided with a hrass appendage which contains a duct, ch>sed at will by a cock, wc introduce a little water, so that the glass may be moistened within by a few drops. The balloon is then screwed to a compressing pump, and so much air is pumped pig, 12. in that the tension in the interior of the balloon shall amount to about three atmospheres. 11&q
. Annual report of the Board of Regents of the Smithsonian Institution. Smithsonian Institution; Smithsonian Institution. Archives; Discoveries in science. PRINCIPLES OF THE JIECIIANICAL THEORY OF HEAT. 271. •which is wrapped around with wire and provided with a hrass appendage which contains a duct, ch>sed at will by a cock, wc introduce a little water, so that the glass may be moistened within by a few drops. The balloon is then screwed to a compressing pump, and so much air is pumped pig, 12. in that the tension in the interior of the balloon shall amount to about three atmospheres. 11" the cock be now closed, and the balloon be unscrewed and laid in some warm place, whether in the vicinity of a stove or in the sunshine, the vapors in the interior will, after a while, have acquired the elasticity corresponding to the temperature, and appear perfectly transparent. If the cock bo now opened, air and vapor will rapidly escape from the balloon, and the latter will l)e tilled with a. thick mist. In a somewhat altered form, the experiment ad- mits of being executed as follows : Let the bell of an air-pump be sprinkled on the inside with a little water, and after being placed on the plate of the pump, be left some time in a rather warm chamber. As soon now as we begin to discharge the air, a white mist will be formed within the bell. A corresponding experiment has been instituted by Hirn on a large scale. A straight copper cylinder, two metres long and 15 centimetres in diameter, v/as closed at both ends by flat plates, in the middle of w-hich were openings two centimetres wide and closed by plates of glass cemented therein. This cylinder was on one side placed in connection with a steam-boiler, while on the other it bore a discharge tube which was furnished with a wide cock. Into the cylinder was now introduced steam of a higli tension, while the escape-cock was only "partially opened, so that all the air might find an issue. The highly condensed vapor,
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