This collection of letters between Darwin and a variety of correspondents shows his perspective on the use and importance of the microscope.
Letter 207 — Darwin, C. R. to Fox, W. D., 23 May 1833
Darwin tells Fox to buy a microscope. He says invertebrate marine animals are his delight. The pleasure of working with a microscope ranks second only to geology.
Letter 1018 — Darwin, C. R. to Hooker, J. D., [6 Nov 1846]
Darwin tells Hooker, if he pays him a visit, to bring some work and if he has anything under his microscope, he will “take advantage of your wicked offer of assistance”. The letter is full of observations on barnacles and he would like to meet Hooker in London.
Letter 1166 — Darwin, C. R. to Owen, Richard, [26 Mar 1848]
Darwin describes in detail to Owen his new microscope and its advantages over the one he used on the Beagle for dissecting. He suggests Owen might discuss the topic [in his contribution to J. F. W. Herschel, ed., Manual of scientific enquiry (1849)].
Letter 1167 — Darwin, C. R. to Henslow, J. S., [1 Apr 1848]
Darwin ends by suggesting that if Henslow is starting off a young naturalist with tools, he recommends him to Smith & Beck of 6 Colman St. City for a simple microscope. Darwin finds this microscope “wonderfully superior”.
Letter 1174 — Darwin, C. R. to Hooker, J. D., 10 May 1848
Darwin discusses his barnacle work. He is confident of his species theory as result of applying it to cirripede sexual systems. He tells Hooker that he sent Owen an account of his new simple microscope, which he finds even better than Hooker’s. He also mentions his new 18 object glass.