[283] Or, more strictly speaking, unless its thickness be less than twice the range of the molecular forces.
[284] It follows that the tension, depending only on the surface-conditions, is independent of the thickness of the film.
[285] This simple but immensely important formula is due to Laplace (Mécanique Céleste, Bk. x. suppl. Théorie de l’action capillaire, 1806).
[286] Sur la surface de révolution dont la courbure moyenne est constante, Journ. de M. Liouville, VI, p. 309, 1841.
[287] See Liquid Drops and Globules, 1914, p. 11. Robert Boyle used turpentine in much the same way. For other methods see Plateau, op. cit. p. 154.
[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. 29–39, 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 Thomson’s Properties of Matter, pp. 151, 152, (ed. 1907).
[292] Kühne, Untersuchungen über das Protoplasma, 1864, p. 75, etc.