Sources and Sinks

Abstract

MR. DUFTON' experiment (NATURE, June 23, p. 522) showing attraction between a source and an equal sink illustrates forcibly a remark by Mr. A. Mallock in the issue for August 19, 1920, p. 777: In most problems relating to the actual phenomena exhibited by fluids in motion, the simple assumptions on which the hydrodynamical theory of text-books rests are insufficient, and experiments are required. At my suggestion Mr. R. Schlapp has recently been making some experiments on the forces between sources and sinks. The vertical limb (about 80 cm. in length) of a T-shaped glass tube dipped into a tank of water, and the horizontal portion rested on V supports. One end of this horizontal part was sealed, the other was connected by rubber tubing either to a high-pressure water supply or to a water pump, so that the end of the tube in the tank acted as either a source or a sink. Three types of orifice were used: (a) the open end of the glass tube (internal diameter 0·4 cm.)—this worked well as a sink, but was unsatisfactory as a source; (b) a hollow brass sphere (diameter 2 cm.) with numerous perforations; (c) a short length of rubber tube having the lower end plugged and perforations over about 2 cm. On the whole the last arrangement proved the most convenient, but care had to be taken to ensure that no movement arising from lack of symmetry in the size and spacing of the perforations took place when using an isolated source.