_In a vacuum, however, liquids fall like solids without separation of their molecules._ The _water-hammer_, a model used in scientific schools, illustrates this: the instrument consists of a thick glass tube about a foot long, half filled with water, the air having been expelled by ebullition previous to closing one extremity with the blow-pipe. When such a tube is suddenly inverted, the water falls in one undivided mass against the other extremity of the tube, and produces a sharp metallic sound, resembling that which accompanies the shock of two solid bodies coming suddenly together. NOTE.—The resistance opposed by the air to falling bodies is especially remarkable in the case of liquids. The Staubbach in Switzerland is a good illustration; an immense mass of water is seen falling over a high precipice, but before reaching the bottom it is shattered by the air into the finest mist. See Parker’s Philosophy, pp. 69-70. It has been ascertained, by experiment, that from rest, a body falling freely will descend 16-1/12 feet in the first second of time, and will then have acquired a velocity, which being continued uniformly, will carry it through 32-1/6 feet in the next second. Therefore if the first series of numbers be expressed in seconds, 1″, 2″, 3″, &c., the velocities in feet will be 32-1/6, 64-1/3, 96-1/2, &c.; the spaces passed through as 16-1/12, 64-1/3, 144-3/4, &c., and the spaces for each second, 16-1/2, 48-1/4, 80-5/12, &c. TABLE. _Showing the Relation of Time, Space and Velocity._ ----------+-----------+--------+------------+------+----------------- Time in | Velocity | |Space fallen| | Whole space seconds of|acquired at|Squares.| through |Space.|fallen through in the body’s|the end of | | in that | | the last second fall. |that time. | | time. | | of the fall. ----------+-----------+--------+------------+------+----------------- 1 | 32·16 | 1 | 16·08 | 1 | 16·08 2 | 64·33 | 4 | 64·33 | 3 | 48·25 3 | 96·5 | 9 | 144·75 | 5 | 80·41 4 | 128·66 | 16 | 257·33 | 7 | 112·58 5 | 160·83 | 25 | 402·08 | 9 | 144·75 6 | 193· | 36 | 579· | 11 | 176·91 7 | 225·17 | 49 | 788·08 | 13 | 209·08 8 | 257·33 | 64 | 1029·33 | 15 | 241·25 9 | 289·5 | 81 | 1302·75 | 17 | 273·42 10 | 321·66 | 100 | 1946·08 | 19 | 305·58 | | | | | ----------+-----------+--------+------------+------+-----------------