270 As Graham said of an allied phenomenon (the so-called blood-crystals of Funke), it ãillustrates the maxim that in nature there are no abrupt transitions, and that distinctions of class are never absolute.ã
271 Cf. Przibram, H., Kristall-analogien zur EntôÙwickeôÙlungsôÙmeôÙchaôÙnik der Organismen, Arch. f. Entw. Mech. XXII, p. 207, 1906 (with copious bibliography); Lehmann, Scheinbar lebende Kristalle und Myelinformen, ibid. XXVI, p. 483, 1908.
272 The idea of a ãsurface-tensionã in liquids was first enunciated by Segner, De figuris superficierum fluidarum, in Comment. Soc. Roy. GûÑttingen, 1751, p. 301. Hooke, in the Micrographia (1665, Obs. VIII, etc.), had called attention to the globular or spherical form of the little morsels of steel struck off by a flint, and had shewn how to make a powder of such spherical grains, by heating fine filings to melting point. ãThis Phaenomenonã he said ãproceeds from a propriety which belongs to all kinds of fluid Bodies more or less, and is caused by the Incongruity of the Ambient and included Fluid, which so acts and modulates each other, that they acquire, as neer as is possible, a spherical or globular form....ã
273 Science of Mechanics, 1902, p. 395; see also Machãs article Ueber die physikalische Bedeutung der Gesetze der Symmetrie, Lotos, XXI, pp. 139ã147, 1871.
274 Similarly, Sir David Brewster and others made powerful lenses by simply dropping small drops of Canada balsam, castor oil, or other strongly refractive liquids, on to a glass plate: On New Philosophical Instruments (Description of a new Fluid Microscope), Edinburgh, 1813, p. 413.