288 Felix Plateau recommends the use of a weighted thread, or plumb-line, drawn up out of a jar of water or oil; Phil. Mag. XXXIV, p. 246, 1867.
289 Cf. Boys, C. V., On Quartz Fibres, Nature, July 11, 1889; Warburton, C., The Spinning Apparatus of Geometric Spiders, Q.J.M.S. XXXI, pp. 29ã39, 1890.
290 J. Blackwall, Spiders of Great Britain (Ray Society), 1859, p. 10; Trans. Linn. Soc. XVI, p. 477, 1833.
291 The intermediate spherules appear, with great regularity and beauty, whenever a liquid jet breaks up into drops; see the instantaneous photographs in Poynting and Thomsonãs Properties of Matter, pp. 151, 152, (ed. 1907).
292 Kû¥hne, Untersuchungen û¥ber das Protoplasma, 1864, p. 75, etc.
293 A Study of Splashes, 1908, p. 38, etc.; Segmentation of a Liquid Annulus, Proc. Roy. Soc. XXX, pp. 49ã60, 1880.
294 Cf. ibid. pp. 17, 77. The same phenomenon is beautifully and continuously evident when a strong jet of water from a tap impinges on a curved surface and then shoots off it.
295 See a Study of Splashes, p. 54.
296 A case which we have not specially considered, but which may be found to deserve consideration in biology, is that of a cell or drop suspended in a liquid of varying density, for instance in the upper layers of a fluid (e.g. sea-water) at whose surface condensation is going on, so as to produce a steady density-gradient. In this case the normally spherical drop will be flattened into an oval form, with its maximum surface-curvature lying at the level where the densities of the drop and the surrounding liquid are just equal. The sectional outline of the drop has been shewn to be not a true oval or ellipse, but a somewhat complicated quartic curve. (Rice, Phil. Mag. Jan. 1915.)