Note 11 — § 2. The Effect of an Electric Field.

Note added during the proof—In the Phys. Zeitsehr. of Feb. 1, A. Garbasso and E. Gehrcke (c. f. note, p. 6) have deduced expressions for which differ from (22) only by a numerical factor of 2 and respectively. The arguments of Garbasso are stated very briefly, but seem of a type similar to those of the present paper. The line of arguments of Gehrcke differs essentially from that used here.