In his letter “Blackett Adopted Earlier Rotation Idea” (PHYSICS TODAY, January 2011, page 10), Thomas Ruedas complains about an error by implication in Greg Good’s article “Rutherford’s Geophysicists” (PHYSICS TODAY, July 2010, page 42). He says Good gave the impression that Patrick Blackett originated the idea that the magnetic field of a rotating body such as Earth or the Sun is produced by its rotation. True, Good could have used better phrasing, but Blackett himself made no such claim; his papers fully acknowledged the long previous history of the subject. Blackett’s 1947 paper includes a reference to Arthur Schuster’s paper of 1891, and his final, 1952, paper on this topic goes back to an obscure German work by Henry Rowland in 1885, presumably reporting the experiment Rowland did in 1875, an experiment that started the ball rolling.
Some years ago I prepared an annotated bibliography “Rotation Theories of the Production of the Magnetic Field of the Earth and Other Bodies”; it is available online at http://www.agu.org/history/mf/contrib/rotation.doc.
