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May 7, 1869.] TRE PHOTOGRAPHIC NEWS. 225 say that the views exhibited this evening were made from | half-size negatives with a Shive instrument, by Mr. Albert Moore, of Philadelphia, who excels in that department of photography. Nineteen of these cameras arc in constant use at his establishment, some of them of mammoth size, making a print 34 by 44 inches. Great care and attention are required to make good solar work. The focus must be exact, and, during exposure, the position of the box altered every minute, so that the sun’s rays, passing through the condensing lens, strike exactly in the centre of the focussing lens. This is easily arranged by having two openings, through which the sunlight passes, cut upon the outside edge of the box, about twelve inches apart, and parallel with the focussing lens. By watching the spot of sunlight on a projection of the box, the appara tus is kept in the right position. Should it be allowed to remain stationary for several minutes, the focus of the con densing lens (altered by the position of the sun) will strike at an angle, causing a blurred image ; there is also danger of fire. Intense negatives are often broken by the heat of the sun, as a long exposure is required. Good negatives should take about forty minutes to make a print. PHOTOGRAPHIC EXPERIMENTS. BY H. J. NEWTON.* Having devoted much time within the last few years ex perimenting in photography, I have been led to read with much interest the experiments of others in the same branch of science. I have, however, observed that photographic experimenters exhibit a phenomenon peculiar to human nature ; it may not be a defect, but it certainly is, in many instances, a serious impediment in the road to truth, or to correct results. I mean the effect upon the mind of a pre conceived opinion, or, at least, a preconceived opinion ex pressed. The expression of an opinion appears to have a power such as nothing else has in shielding the mind ; it sometimes seems like an impregnable fortress, into which the mind retires, and bids defiance alike to reason as to sophistry, whether in physics, metaphysics, theology, or geology ; in fact, any subject upon which the mind can form an opinion appears to be subject to this universal law. I do not pro pose here to attempt an analysis of the reason why it is so, but only to set forth the facts so prominently that some experimenters may be induced to revolve in a larger sphere. I hold it to be the duty of all experimenters to seek wholly for the truth, and the best; not like, I am sorry to say, too many, who work, it would appear, only to defend and fortify some pet formula or process. It may be a legitimate off spring, or it may be an adopted child, only so that they father it, and the public recognize them as its proper and legitimate guardian. It becomes to them then, like the mother’s firstborn, a wonder, a marvel, and they the parent of it! Such turn with contempt from anyone who is pre sumptuous enough to question the perfection of their little idol, either forgetting, or having never known, that human reason has not the prerogative of infallibility, or any way of arriving at infallible conclusions, except in one way, and that involves the necessity of reducing your problem to a mathematical proposition or its equivalent. It must be in a form susceptible of absolute proof. Those who have a monied interest in any secret or patented process are excusable for a certain amount of special pleading in behalf of their interests ; but those who have no interest, except what pride or egotism suggests, have nothing to offer but the weakness and frailty of human nature ; and it is a tacit acknowledgment that they are unequal to the conflict necessary to resist its unreasonable commands. Some have a particular process, old and defunct, which they periodically exhume and exhibit to the photographic public in an obituary notice, or what strongly reminds you of one. Such * Read before the Photographic Section of the American Institute. may possibly be ornaments to photographic literature, but they are rarely, if ever, useful. They are always eager to defend their hobby against any innovation ; no rivalry is tolerated ; they condemn everything that suggests any change or improvement; no amount of argument would induce them to change their formulae or peculiar mode of operation. We have an example of such in those who deny the utility of bromide in collodion. They will have only iodide ; they will not use a bromo-iodized collodion, or even try it; they claim to know more by theory than others can learn by experimenting. I hold that no one has the right to deny or to call in question the claims of any one, when such claims are founded on actual experiments, or even to put them in unfavourable contrast with other processes which produce similar results, unless they have tested the correctness of the conclusions in the manner described in the particular experiment. There would, of course, be exceptions to this rule, in eases when statements were made in direct conflict with well-known and established physical laws. In dry plates, however, very little is known positively what is the exact thing in a solu tion that acts upon the sensitive film to preserve it; conse quently, experimenters have a wide field from which to gather their material for experimenting. There is not enough known upon the subject for any one to tell what effect tea or coffee would have upon the plate without trying it, and so with a multitude of other vegetable substances. It would seem proper, therefore, in giving some results of experiments, to state the failures as well as results which are deemed successful. The tannin plate has usually been recognized as the standard by experimenters, as it was the first really good and successful dry plate. Experiments have not been made with a view of finding something which would keep a plate longer than tannin, but to find some thing which was as good a preservative as tannin, and, at the same time, possessed qualities which would enable it to retain its sensitiveness. A number claim to have succeeded in producing such plates. I have tried almost every published formula, and I have no hesitation in saying that there are a large number of formulas which will, if carefully worked, produce plates superior, in every respect, to tannin. The keeping qualities, of course, can only be decided by time; it is a fair infer ence, however, that if a plate will keep through the summer months without suffering any detrimental change, that it is good for a year. The coffee plates have been kept two years without showing any change, which is much longer, under ordinary circumstances, than would ever be required. After a plate has kept well for a year, the fact that it will keep another adds nothing to its value. As I observed before, the effort of those experimenting with dry plates has been to discover something that would make them approxi mate as near as possible in their sensitiveness to wet ones. The great drawback to the tannin plates has been their great lack of sensitiveness. {To be continued.) Zerent Aateuts. PHOTO-MECHANICAL PRINTING PROCESSES. BY ALEXANDER ARGAMAKOFF AND BASILE BAULER. The following patent is for improved modes of securing photo-engraving, phototypic, and photo-lithographic print ing surfaces. Unless we are in error, some parts of the principle of Mr. Woodbury’s patent are comprised in this specification. This invention has for its object improvements in the pro duction, by means of photography, of printing surfaces adapted to lithography, typography, and chromotype. By application to lithography is to be understood the transfer of the drawing from the copper plate to the stone.