2 The holes in the cylinders are bored obliquely, as shown in Fig. 4, which causes them to remain at any desired position on the cord and allows them to be freed to move up and down by slackening the cord for a moment.
3 ‘On the Homogeneous Division of Space,’ by Lord Kelvin, Royal Society Proceedings, vol. lv, Jan. 18, 1894.
4 Similar curves are said to be parallel when the tangents to them at corresponding points are parallel.
6 ‘On the Division of Space with Minimum Partitional Area,’ Philosophical Magazine, vol. xxiv, 1887, p. 502, and Acta Mathematica of the same year.
7 A. Levy, Edinburgh Philosophical Journal, April, 1822; Whewell, Phil. Trans. Royal Society, 1825; Miller, Treatise on Crystallography.
8 I call any geometrical figure, or group of points, chiral, and say that it has chirality, if its image in a plane mirror, ideally realized, cannot be brought to coincide with itself. Two equal and similar right hands are homochirally similar. Equal and similar right and left hands are heterochirally similar or ‘allochirally’ similar (but heterochirally is better). These are also called ‘enantiomorphs,’ after a usage introduced, I believe, by German writers. Any chiral object and its image in a plane mirror are heterochirally similar.
9 Philosophical Magazine, vol. xx, 1885, second half year, p. 469, and British Association Report, 1885, Aberdeen, p. 896.
10 The solids of the photograph are castings in fine plaster of Paris from a scalene tetrahedron of paraffin wax, with its corners and edges rounded, used as a pattern.
11 ‘A twin-crystal is composed of two crystals joined together in such a manner that one would come into the position of the other by revolving through two right angles round an axis which is perpendicular to a plane which either is, or may be, a face of either crystal. The axis will be called the twin-axis, and the plane to which it is perpendicular the twin-plane.’ Miller’s Treatise on Crystallography, p. 103. In the text the word ‘twin-plane,’ quoted from the writings of Stokes and Rayleigh, is used to signify the plane common to the two crystals in each of the cases referred to: and not the plane perpendicular to this plane, in which one part of the crystal must be rotated to bring it into coincidence with the other, and which is the twin-plane as defined by Miller.
12 ‘A clear transparent crystal of potassium chlorate, from which the inevitable twin-plate had been ground away so as to reduce it to a single crystal film about 1 mm. in thickness, was placed between pieces of mica and laid on a thick iron plate. About 3 cm. from it was laid a small bit of potassium chlorate, and the heat of a Bunsen burner was applied below this latter, so as to obtain an indication when the temperature of the plate was approaching the fusing-point of the substance (359° C according to Prof. Carnelly). The crystal plate was carefully watched during the heating, but no depreciation took place, and no visible alteration was observed, up to the point at which the small sentinel crystal immediately over the burner began to fuse. The lamp was now withdrawn, and when the temperature had sunk a few degrees a remarkable change spread quickly and quietly over the crystal plate, causing it to reflect light almost as brilliantly as if a film of silver had been deposited upon it. No further alteration occurred during the cooling; and the plate, after being ground and polished on both sides, was mounted with Canada balsam between glass plates for examination. Many crystals have been similarly treated with precisely similar results; and the temperature at which the change takes place, has been determined to lie between 245° and 248°, by heating the plates upon a bath of melted tin in which a thermometer was immersed. With single crystal plates no decrepitation has ever been observed, while with the ordinary twinned-plates it always occurs more or less violently, each fragment showing the brilliant reflective power above noticed.’—Nature, May 20, 1886.
16 WidmanstÄtten, 1807. Leydolt (1855, Wien. Akad. Ber. 15, 59, T. 9, 10. Baumhauer, Pogg. Ann. 138, 563 (1869); 140, 271; 142, 324; 145, 460; 150, 619.) For an account of these investigations, see Mallard, TraitÉ de Crystallographie (Paris, 1884), Tome II, chapitre xvi.
17 More exactly .9525, being 3/4 × cot 38° 13'; see p. 53.
18 J. and P. Curie and C. Friedel, Comptes Rendus, 1882, 1883, 1886, 1892.
19Allgemeine Theorie der piËzo- und pyroelectrischen Erscheinungen an Krystallen. W. Voigt, KÖnigl. Gesellschaft der Wissenschaften zu GÖttingen, August 2, 1890.
