_Improvement in Positives._--I have great pleasure in communicating to you an improvement in the process of taking positives, which may not be uninteresting to some of your readers, and which ensures by far the most beautiful tints I have yet seen. I take three ounces of the hyposulphite of soda, and dissolve it in one pint of distilled or rain water; and to this I add about one or one and a half grains of pyrogallic acid, and seventy grains {534} of chloride of silver; which must be squeezed up between the finders facilitate its solution and separate the lumps, which, in their dry state, are tough, and not easily pulverised. The whole is then to be set aside for a week or two in a warm place. The solution, at first colourless, becomes brown, and ultimately quite opaque; in this state it is fit for use, and the longer kept the better it becomes. I generally use French paper for this process, and, according to the time of immersion, obtain fine sepia or black tints; the latter requiring long over-exposure to the light, and proportionately long exposure to the action of the liquid; which however will be found, particularly when old, to have a more rapid action than most other setting liquids, and has the merit of always affording fine tints, whatever the paper used. I imagine the pyrogallic acid to possess a reducing influence on the salts of silver employed; but this effect is only produced by its combination with the hyposulphite of soda and chloride of silver. I may add, that in any case the pictures should be much overdone before immersion, as the liquid exerts a rapid bleaching action on them; and when the liquid becomes saturated, a few crystals of fresh hyposulphite will renew its action. F. MAXWELL LYTE. Florian, Torquay. P. S.--In answer to a COUNTRY PRACTITIONER, he will find great assistance in choosing his lens by laying it on a sheet of blue wove post paper, when he will immediately perceive the slightest yellow tinge in the glass, this being the fault which frequently affects many well-ground and well-made lenses. Of course, for sharpness of outline he must be guided entirely by experiment in the camera; but where weakness of action exists, it most frequently arises from this yellow colouration, and which the manufacturers say is very difficult to avoid. [MR. LYTE having sent with his communication a positive prepared in the manner described, we are enabled to corroborate all he says as to the richness and beauty of its tints.] _Cheap Portable Tent._--M. F. M. inquires for a cheap and portable tent for working collodion out of doors. I have been using one lately constructed on the principle of Francis's camera stand. It has a good size table, made like the rolling patent shutters; and it is not necessary to stoop, or sit down at your work, which is a great consideration on a hot day: you may get them of any respectable dealer in photographic apparatus; it is called Francis's Collodion Tent. H. D. FRANCIS.