effect of thickness of lenses was shown by a diagram of the ingenious
method of Mr. F. Wenham, who had long ago by this means corrected
spherical aberration in microscopic objective. The construction of
portrait lenses was next gone into, the influence of the negative
element of the back lens being especially noted. A method was then
referred to of making a rapid portrait lens cover a very large angle by
pivoting at its optical center and traversing the plate in the manner of
the pantoscopic camera. The lecturer concluded by requesting a careful
examination of the valuable exhibits upon the table, kindly lent for the
occasion by Messrs. Ross & Co.

* * * * *




IMPROVED DEVELOPERS FOR GELATINE PLATES.

By Dr. Eder.


We are indebted to Chas. Ehrmann, Esq., for the improved formulas given
below as translated by him for the _Photographic Times_.

Dr. Eder has for a considerable time directed especial attention to the
soda and potash developers, either of which seems to offer certain
advantages over the ammoniacal pyrogallol. This advantage becomes
particularly apparent with emulsions prepared with ammonia, which
frequently show with ammoniacal developer green or red fog, or a fog of
clayish color by reflected, and of pale purple by transmitted light.