Sent by John Aitken, Ardenlea, Falkirk, Scotland to Alfred Russel Wallace [address not recorded] on 7 April 1899.
Re. light, atmospheric particles and the causes of the blue colour of sea water and sky; 2 ff., back of f. 2 annotated in Alfred Russel Wallace's hand 'See Tyndall in Nature vol. 1. ... colours of water and air'.
A typical letter .