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Footnote 158:

J. J. Thomson, Phil. Mag., =44=, 293, 1897.

Footnote 159:

R. A. Millikan, Phys. Rev., =2=, 109, 1913.

Footnote 160:

P. Zeeman, Phil. Mag., =43=, 226, 1897.

Footnote 161:

H. A. Lorentz, Phil. Mag., =43=, 232, 1897.

Footnote 162:

S. J. Barnett, Phys. Rev., =6=, 239, 1915, and =10=, 7, 1917.

Footnote 163: