Electrically driven jets BY SIR

Fine jets of slightly conducting viscous fluids and thicker jets or drops of less viscous ones can be drawn from conducting tubes by electric forces. As the potential of the tube relative to a neighbouring plate rises, viscous fluids become nearly conical and fine jets come from the vertices. The potentials at which these jets or drops first appear was measured and compared with calculations. The stability of viscous jets depends on the geometry of the electrodes. Jets as small as 20 ,um in diameter and 5 cm long were produced which were quite steady up to a millimetre from their ends. Attempts to describe them mathematically failed. Their stability seems to be due to mechanical rather than electrical causes, like that of a stretched string, which is straight when pulled but bent when pushed. Experiments on the stability of water jets in a parallel electric field reveal two critical fields, one at which jets that are breaking into drops become steady and another at which these steady jets become unsteady again, without breaking into drops. Experiments are described in which a cylindrical soap film becomes unstable under a radial electric field. The results are compared with calculations by A. B. Basset and after a mistake in his analysis is corrected, agreement is found over the range where experiments are possible. Basset's calculations for axisymmetrical disturbances are extended to those in which the jet moves laterally. Though this is the form in which the instability appears, calculations about uniform jets do not seem to be relevant. In an appendix M. D. Van Dyke calculates the attraction between a long cylinder and a perpendicular plate at a different potential. It was pointed out 369 years ago by William Gilbert (i6oo) that a spherical drop of water on a dry surface is drawn up into a cone when a piece of rubbed amber is held at a suitable distance above it. This phenomenon has recently (Taylor I964) been subjected to theoretical treatment and it was shown that a conducting fluid can exist in equilibrium in the form of a cone under the action of an electric field but only when the semivertical angle is 49.3?. Apparatus was constructed in which the necessary field could be set up and very nearly conical fluid surfaces or interfaces between two fluids were formed for which the semivertical angle was close to 49.3O. An uncharged drop …