Page 127: "in the magnetic meridian, then"--had "meridan." Page 128: "mainly of the postscript, with"--had "postcript." Page 134: "paper of April 2, 1821,[22] is quite"--had "1921." Page 135: "thermoelectric circuits, where"--had "thermoelectirc." Page 135: "arrangement has resulted."--had "arragnement." Page 135: "King of the American Institute of Physics."--had "Physic." Footnote 13: "_Geschichte der Elektrizitaet_"--had "Elektrizitat." Footnote 16: "_Journal fuer Chemie und Physik_"--had "and." Footnote 24: "The German word _Kette_"--had "work." Questionable spellings have been retained as follows: Page 125 and Index: J. B. [Johann Bartholomacus] Tromsdorff--should be Johann Bartholomaeus Trommsdorff? Page 129: "sulphur, phosphorous and carbon..."--should be "phosphorus" but may be misspelled in the quoted material? Footnote 20: "Sur le Multiplier electro-magnetique..."--should be "Multiplicateur"?