He was forced to retire early, in 1888, because of partial blindness, but continued to take an active part in local government and church life in St Pancras, London, where he lived.
Prosser had in mind to write a history of invention, written around the abstracts of British Patent Specifications, but the project never got further than the planning stage.
More of Prosser's papers are in Birmingham and Manchester reference libraries, having been presented either by himself in his lifetime or by his family after his death.
The on-line catalogue of the National Archives lists small collections of Prosser's papers for patentees in the South West of England, Northamptonshire and Buckinghamshire.
Prosser was a pioneer of the study of technical history, and his published biographies and manuscript records are an incomparable source for present-day researchers.