[13] Nature, May 20, 1886.
[14] Philosophical Magazine, 1888, second half year, p. 260.
[15] See [foot-note] to § 22 above.
[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.
[19] Allgemeine Theorie der piëzo- und pyroelectrischen Erscheinungen an Krystallen. W. Voigt, Königl. Gesellschaft der Wissenschaften zu Göttingen, August 2, 1890.
[20] Wiedemann, Annalen, 1892, xlv, p. 923.
[21] Generally miscalled ‘rotational.’
[22] See [foot-note (2)] to p. 54 above.