The book “the theory of perspective demonstrated: The Theory of Perspective Demonstrated; By Planes, Lines, and Points, Made Use of in This Art, Are Shewn in the True Positions in Which They Are to Be Considered” by John Lodge Cowley (1719-1797), published 1765 in London can be found in the Eth Bibliothek or online (https://www.recherche-portal.ch/primo-explore/search?vid=ZAD&query=any,contains,John%20Cowley%20The%20theory%20of%20perspective%20demonstrated&lang=de_DE).
