Letter, from Richard Anthony Proctor to Sir John Herschel, dated at 5 Trigon Road, Kennington Autograph letter signed by sender. Elaborates on his hypothesis that all forms of nebulae are part of the Milky Way and on his 'twisted-stream theory' of the Milky Way's structure. Favors view that dark matter is relatively common in space and that it extinguishes light from distant objects. Proposes method of measuring stellar diameters. 9 August 1869