Pritchard set up as an optician, and also sold microscopes and microslide preparations. These slides he prepared by studying the microscopic organisms that he saw, and identifying and labelling them. Starting in 1830, he collaborated with C.R. Goring to produce beautifully illustrated books showing the " animalcules " visible through the microscope. His shops were in central London, more towards The City than the West End, variously at 162 Fleet Street, Pickett Street and 312 & 263 The Strand. The Oxford Dictionary of National Biography says his List of 2000 Microscopic Objects (1835) "is very important in the history of microscopy... his History of the Infusoria (1841) was long a standard work, and the impetus it gave to the study of biological science cannot be overestimated." (" Infusoria " is a term then current for aquatic micro-organisms.) This latter book was enlarged and revised by John Ralfs and other botanists; Pritchard in turn condensed Ralfs's contribution on the diatomaceæ (diatoms, a type of phytoplankton), and wrote many books and articles on "natural history as seen through the microscope, on optical instruments, and on patents" He issued the exsiccata work British Mosses.