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250 THE PHOTOGRAPHC NEWS, [May 21, 1869. FIELD WORK WITHOUT A TENT. Dear Sir,—Whether Mr. Barrett's letter (which appeared in your last number) in reference to my photo-camera- Jucida was written in a friendly spirit, or not, I cannot tell; but, as in that letter he endeavours to convey the- idea that my plan is defective, inasmuch as that, during the very short time that it takes to insert the blotting-paper pad in the lower end of the protector, the light that did get in would fog the plate; and as many of your readers may be thereby deterred from adopting a thoroughly prac tical invention, I beg to state that, as the protector is black inside, and the opening at the lower end is only large enough to allow it to slide easily on the outside of the bath, and as it extends to from an inch and a-half to two inches below the plate, the light, if any, that does get in, does no harm, being killed, as it were, by the darkness within. Years ago, when I first made the protector, thinking that the light would get in and do harm, I placed a valve at its lower end, that would shut when it was removed from a bath, and open when it was put on one, but by an accident I found it was quite safe to dispense with it. When the plate is ready to be taken out, the pad is held in the left hand near to the bath, and the protector is as easily and as quickly placed upon it as it could be upon the adjoining bath, and there is really no danger attending it, and no hurry required. As to the size of plates that can be worked with my apparatus, I beg to say that it is unlimited. Of course, the bigger the plate the larger the apparatus to carry ; but this must be the case with any other plan, and is, therefore, no disparagement. I may state, however, that large plates can be developed better and cleaner with my plan than by the ordinary dark-room or tent method ; no stains from the developer going unequally over the plate, and no reduced silver at the lower corners from the dark-slide carrier. In the number ot the News for April 23rd, in your remarks upon development by dipping, you stated, as a disadvantage attendant upon it, that each plate developed in a bath lessened the reducing power of the developer. Now, although this may be true in theory, still I have not found it to be a disadvantage in practice. The large quantity of solution, and the fact that every plate dipped leaves some silver in it, no doubt counteracts it. I have many times developed a dozen and a half of plates in an upright bath, when I have been out for a day, and the last has been as good as the first. I have also gone out again and again with the same solution, and with equally good results. The solution is cheap, and it may be as well to filter and to strengthen or renew it, after a dozen plates or so ; but there really is no need to renew it after every plate, as you hinted might be done. In regard to the silver bath, the same objection applies, and, 1 think, with much greater force. It is a much more delicate solution, if I may use the word, than the iron one, and certainly every plate sensitized in it not only robs it of its power, but leaves in it that which is really detrimental, and yet it is tolerated by every photographer in the world. I therefore think that they should not object to a dipping bath for development, on the ground of its losing power from the cause alluded to. Hoping that you may be able to find a corner in your valuable journal for the above, I beg to subscribe myself yours respectfully, Wm. Whiti.no. CRACKED NEGATIVE FILMS. Sir,—Permit me to make a correction in your report of what I said in the discussion which took place at the meet ing of the Photographic Society last Tuesday. The sentence I refer to, as reported in your Journal, runs thus “ Cracks in the collodion film had, unfortunately, been occasionally seen ever since the introduction of ths collodion process, no matter what collodion or what varnish had been used, without the fault being due to either, but rather to the incompatibility of the same two samples when used in conjunction.’’ This last sentence should have been: “ but rather to the incompatibility of some simples^ when used in conjunction.” I referred, of course, to the use of a varnish not quite agreeing with the sample of collodion used For example: some collodions are made with pyroxyline very easily acted upon by strong alcohol, almost to solution, whilst other samples would be quite unaffected by such a solvent. It seems to me that a varnish should be made with a spirit having about the same specific gravity as that used in the manufacture of the collodion, supposing the pyroxyline to be of that kind not easily acted upon by alcohol. It is also important that the spirit should be pure, not methy lated, for it is well known that the solvent power of methy lated spirit is greater on some kinds of pyroxyline than on others. I cannot think that a varnish which possesses a power only just short of acting as a solvent on the body with which it is to be brought into contact is a suitable one to use. Most negative varnishes will bear the addition of a little water, and, where a tendency to solution of the film is shown, this dilution might be advantageously made. I purposely abstained from taking up the time of the meeting by recapitulating the many little points, attention to which gives the photographer, comparatively, an immu nity from the terrible annoyance under discussion, because all these things may be found in any treatise on the subject; moreover, it would have been puerile to have re ferred to them. The nature of the surface of the glass itself, alluded to by Mr. Dallmeyer, is deserving of consideration. I have myself drawn attention to this subject at page G5 of my treatise. It may, probably, not be generally known how easily the surface of plate glass becomes disintegrated by the continued and combined action of heat and moisture. The best kind of patent plate glass, if kept in an ordinary box, becomes ruined in India in about twelve months, or even in less time. Messrs. Chance are quite aware of this, and, I believe, are unable, at present, to manufacture a glass that will stand the exposure referred to. Now, as such is the case, how difficult, if not impossible, it must be to thoroughly restore the surface of old glass plates that have been used for negatives, whether varnished or other wise! Nothing short of re-polishing at the glass works would effectually do this. I know that the very common practice of using up old varnished negative plates is a fer tile source of queer stains, quite abnormal. This practice is, perhaps, also objectionable on other grounds, and may prove to be one source of cracking of the negative film. The subject is important, and might be very easily en larged upon. I fear, however, that I have already taken up too much of your space; at any rate, I have deviated from the object I first had in addressing you.—Yours, &c., May Uth, 1869. R. W. Thomas. 4rorecdings of Societies. South London Photographic Society. The usual monthly meeting was held in the City of London College on the evening of Thursday, the 13th inst., the Rev F. F. Statham, M.A., F.G.S., in the chair. The minutes of a former meeting having been read and con firmed, Messrs. Schtnerl, F. H. Warlich, and J. D. Newsome, of Batley, were duly elected members of the Society. * We are obliged to Mr. Thomas for correcting a printer s error which had escaped our notice.—ED,
