Andrew Pringle, Practical Photo-micrography: By the Latest Methods, Scovill & Adams Company, 1890, pg. 9, accessed via Google books, http://books.google.com/books?id=DPoJAAAAMAAJ&pg=PR9 (accessed 06/18/2015)
Jennifer Tucker, Nature Exposed: Photography as Eyewitness in Victorian Science, JHU Press, Jun 20, 2013 pg. 177, accessed via Google books, http://books.google.com/books?id=dUcDAAAAQBAJ&pg=PA177" target="_blank">website</a>.