PREFACE TO THE THIRD EDITION.
The rapid and unexpected sale of the entire second edition of this Manual has induced the author to lay the Third Edition before the Public. Although but little time has elapsed since the second, yet there have been some new developments which it has been thought best to give, as conducive to the interests of the practitioner. The manipulations have been given somewhat more in detail than in the Second Edition.
All that would have a tendency to confuse the reader has been carefully avoided, and only the plain methods for operating laid down. The work is intended for the beginner in the glass process of producing Heliographic pictures.
S. D. H.
New York, February 1st, 1857.