1. Presented before the joint meeting of the American Physical Society, the American Astronomical Society, and Sections B (Physics) and D (Astronomy) of the American Association for the Advancement of Science, Washington, D.C., December 30, 1924.
2. See footnote 1.
3. Terr. Mag. and Atmos. Elec., vol. 29 (1924), pp. 23–32 and 161–186
4. Table I. was derived from the values of s given in extenso in the author's Table 7, p. 171, Terr. Mag., vol. 29, p. 171.
5. See Fig. 2, Terr. Mag., vol. 29, p. 31.