|Blackett's principal period of research on this topic was 1946-1951. His work on cosmic rays and their origin had let to an interest in astrophysics and the possible influence of magnetic fields on phenomena in electron showers. Further investigation led Blackett to postulate a proportional relationship between magnetic moment and angular momentum, which might constitute 'a possible general law of Nature for all massive rotating bodies'. This hypothesis, formulated in his 1947 paper published in 'Nature' (R.S. 56) attracted very wide attention among the general public as well as in scientific circles (See C.68-71).
Experiments to verify the hypothesis were devised and undertaken, Blackett's own chief contribution being the construction of a highly sensitive magnetometer which eventually gave a negative result and thus disproved the general validity of the earlier theory. (See C.9-12 and note) The sensitivity of the apparatus, however, enabled weak magnetic fields to be detected, and was thus admirably suited to the work on paleomagnetism to which Blackett turned his attention. (see C.72-268 and the introductory note). Blackett's letters to J.W. Warwick, M. Farbstein (C.64) and W. Sullivan (J.97) give his account of his hypothesis and its history.
See Bernard Lovell, 'P.M.S. Blackett: A Biographical Memoir', Royal Society: 1976, pp39-44, and R.S. 54, 56, 60, 61, 62,64
The material is presented as follows:
C.1-29 Working papers, notes, lectures and publications relating to Blackett's hypothesis on magnetic spin and the devising of apparatus and experiments to test it. presented chronologically, retaining Blackett's folders and descriptions as far as possible. 1946-1954
C.30-40 Noteboks at manchester and Imperial College, by Blackett and his assistants. 1947-1954
C.41-71 Correspondence on magnetic spin 1946-1973