er of the paper,
5. The diameter of the diaphragm,
6. Its distance from the lens, and
7. The diameter, focal length, and maker of the lens,

would, if carefully and honestly stated by some twenty or thirty
photographers, be extremely valuable. Of this there can be little doubt,
and we hope that our scientific photographic friends, will respond to this
suggestion. We for our parts are ready to receive any such communications,
and will, at the end of the month, collate and arrange them in such form as
may best exhibit the results. It is obvious that, in a matter of such a
nature, _we_ at least should be furnished with the names of our
correspondents.

_The Ceroleine Process._--The unfavourable state of the weather has
prevented me from making many experiments as to the value of the process
given in your 234th Number, but I have seen enough to convince me that it
will effect a great saving of trouble, and be more sensitive than any
modification of Le Gray's process that has yet been published. It will,
however, be rather more expensive, and, in the hands of persons
unaccustomed to chemical manipulations, rather difficult; but the solutions
once made, the waxing process is delightfully easy.

WILLIAM PUMPHREY.

_On preserving the Sensitiveness of Collodion Plates._--_The Philosophical
Magazine_ of the present month contains a very important article by Messrs.
Spiller and Crookes upon this great desideratum in photographic practice.
We have heard from a gentleman of considerable scientific attainments,
that, from the few experiments which he had then made, he is convinced that
the plan is quite feasible. We of course refer our readers to the paper
itself for fuller particulars as to the reasoning which led the writers to
their successful experiment, and for all enumeration of the many advantages
which may result from their discovery. Their process is as follows:

"The plate, coated with collodion (that which we employ contains
iodide, bromide, and chloride of ammonium, in about equal proportions),
is made sensitive by immersion in the ordinary solution of nitrate of
{430} silver (30 grains to the ounce), and after remaining there for
the usual time, is transferred for a second solution of the following
composition:

Nitrate of zinc (fused) 2 ounces.
Nitrate of silver 35 grains.
Water 6 ounces.

The plate must be left in this ba