IF a capillary tube, A, Fig. 1, with a wedge-shaped cut in it at a distance of about 10 mm. from its upper end, at right angles to, and deep enough to make a breach in one side of its aperture, is lowered slowly into water the rising column of water pauses for an instant when it reaches the gap, which is necessarily higher than the surface of the water into which the tube is being dipped, and then leaps past it and rises to the top of the aperture.