OF the two writers, both have zealously followed photog raphy as something more than a mere amusement, for a con siderable number of years. One of the writers has studied the science from a theoretical and experimental point, while the other writer's attention has been almost entirely directed to the production of practical results by the processes known, and by each process as it has been given to the world. As joint authors, therefore, we trust that our joint work may be acceptable to the photographic public not as replacing, or superior to, other works, but rather as filling a place not occu pied by any other work. The chief claim made for our work is that every word we have written in it refers to subjects with which we are personally and intimately acquainted; not a direction nor a formula is given on trust, every one has been successfully used by one or other of us, in most cases we have both used the formulae found in this book.
