Folder labelled 'Origin of Cosmic Rays' Includes: Numerous sets of manuscript notes by Blackett; several are headed 'Varenna', probably notes taken by Blackett at cosmic ray conference there. Notes on the literature. 7pp typescript by C.B. Wheeler (probably report on research) with sub-headings 'The origin of primary cosmic radiation', 'The rate of thermonuclear reactions', 'Impulsive fuse-blowing', 'Water stabilised high-power arcs'. N.B. Outline of lecture by Blackett delivered in Manchester, revised and delivered to Royal Meteorological Society, 1950, has been extracted and listed separately. See B.107 c.1949-1955