R. A. Millikan, V. H. Gottschalk, and M. J. Kelly
Phys. Rev. 15, 157 (1920) - Published 1 March, 1920
H. A. Wilson
Phys. Rev. 15, 178 (1920) - Published 1 March, 1920
Phys. Rev. 15, 206 (1920) - Published 1 March, 1920