Some resources on Darwin's microscopes
W A S Burnett and L V
Martin, Microscopy, 1992, vol. 36,
part 8, 604-627.
An excellent article which discusses Darwin's microscopes in
some detail. Microscopy is the Journal of the
Quekett Microscopical Club.
The Quekett Microscopical Club Journal 'Microscopy' regularly has authoritative articles on all aspects of the history of light microscopy and microscopists.
'Single Lens: The Story
of the Simple Microscope' by B J Ford, Heinemann, London,
1985. 182 pages. ISBN 434 26844 5.
An easy to read but authoritative account of the contribution
Anton van Leeuwenhoek and others made to science using a
single lens microscope. Some aspects of Darwin and his
microscopes are covered in this book.
'A Treatise on the Construction, Capabilities and Proper Use of Smith, Beck and Beck's Achromatic Microscopes' by Richard Beck, London, 1865. 'Single microscopes. Darwin's Instrument' p.102 - 104. Description and illustrations.
Charles Darwin's microscopes - Illustrated resource on the website of the Whipple Museum of the History of Science, Cambridge, UK.