BELL SYSTEM TECHNICAL JOURNAL 



Fig. 9 — MacGregor-Morris, 1902 — -tube by Cossor."* 



Fig. 10— Ryan, 1903— tube by ]\Iuller-Uri.^ 



II ^ 



^ 



L 



^ 



l^tA'xV.MO^.SJ 



Fig. 11 — Roschansky, 1911.* 



Fig. 12 — Broughton, 1913 — tube by Max Kohl. 



^ MacGregor-AIorrls, Engineering, 1902, 73, p. 754. 



7 Ryan, H. J., Am. Inst. El. Eng., Trans., 22, p. 539, 1903. 



» Roschansky, D., Aym. d. Phys., 36, p. 281, 1911. 



9 Broughton, H. H., Electrician, 72, p. 171, 1913. 



