[1] See the English translation by the Gilbert Club of Gilbert's _De
magnete_, p. 49 (London, 1900).
[2] See Lord Kelvin, "Report on Electrometers and Electrostatic
Measurements," _Brit. Assoc. Report_ for 1867, or Lord Kelvin's
_Reprint of Papers on Electrostatics and Magnetism_, p. 260.