^{page 34 note *} These Proceedings, 45, 1925, p. 166.

^{page 37 note *} Publ. des aslroph. Obs. zu Potsdam, 22, 1913, Nr. 67.

^{page 37 note †} Opt. Soc. Amer. Journ., 7, 1923, p. 1079 ; 11, 1925, p. 319 ; 12, 1926, p. 321.

^{page 39 note *} Monthly Notices R.A.S., 75, 1915, p. 159.

^{page 40 note *} Ilford Beta Filter.

^{page 41 note *} Proc. Roy. Soc. Lond., 98, 1920, p. 154.

^{page 44 note *} Slade, R. E. and Higson, G. I., loc. cit., pp. 163 Google Scholar, 167, 168.

^{page 46 note *} Cf. Arons, , Ann. d. Physik, 58, 1896, p. 91.Google Scholar

^{page 46 note †} Weber ibid., 45, 1914, p. 801.

^{page 46 note ‡} See Nutting, P.G., Phil. Mag., 26, 1913, p. 423.CrossRefGoogle Scholar

^{page 47 note *} It may be noted here that the same reasoning applied in the case of action by a single quantum gives the value unity for q at low densities.

^{page 48 note *} Opt. Soc. Amer. Journ., 12, 1926, p. 329.

^{page 48 note †} The Wratten process emulsion used by Jones, Huse, and Hall gives, however, exceptionally low values for p. Thus, in their experiments, the value of p corresponding to an exposure of 30 seconds is about 0·6, whereas the batch of Ilford process plates used by the writer gave the value 0·95. See also Channon, , Brit. Journ. Phot., 73, 1926, p. 733.Google Scholar [Feb. 5, 1927.]

^{page 48 note ‡} Sheppard, S. E., “Photography as a Scientific Implement” (1923), p. 179.Google Scholar

^{page 48 note §} Piper, C.W., Brit. Journ. Phot., 55, 1908, p. 195.Google Scholar

^{page 48 note ‖} Ann. der Physik., 77, 1925, p. 495.

^{page 48 note ¶} Cf. Allen, H. S., Photo Electricity, 1st ed., p. 206.Google Scholar