Some modification of the above-which I cut out, with a view to making experiments-would, I think, answer for the production of this striking novelty in photography. The specimens I saw were on a white, and on a beautiful fleshy pink substance, the latter giving a really lovely effect. The mellowness and transparency of these photographs, and their extreme delicacy and softness, must be seen to be fully appreciated. Dr. Boynton, of Syracuse, New York, where he is well known as an able scientific lecturer and geologist, has pointed out that surrounding the earth's conical shadow, which is cast by the rays of the sun, there is probably a stratum of refracted light which may be forming the prismatic shadow of the earth's atmosphere, which, by refraction, separates and disperses the luminous and actinic rays; the former taking a direction near the exterior of the shadow, and the former towards its centre. Such refracted rays falling upon the moon are reflected from its surface. A section of the earth's shadow, and that of its atmosphere, will give two distinct reversed spectra, with the actinic rays nearer the centre of the earth's shadow, and the heating and luminous rays nearer the external portion of the section. During an eclipse the east limb of the moon, on intersecting the earth's shadow, must necessarily first pass through the prismatic rays; so also will the entire surface of the moon be successively subject to the same conditions, until, finally, as its western limb emerges from the earth's shadow, the same prismatic phenomenon will manifest itself in a reversed order. Another interesting effect must not be overlooked-as the moon immerges or emerges into or from this prismatic halo, its entire face is subject in succession to distinct and separate luminous and actinic rays arranged parallel to each other. This being the fact, should we attempt to photograph the moon when near, or partially in, the earth's shadow, some portions of its luminous rays being actinic, while others are not, we would fail to produce a perfect picture of all portions of her surface at the same time. Professor Tillman alluded to a statement made at a meeting of the Astronomical Society of London, that in the photographs of the lunar eclipse, which occurred on the thirteenth of September last, a portion of the unobscured part of the moon was absent. Mr. De la Rue remarked at that meeting, in relation to the nature of this phenomenon, that more of the moon was eclipsed chemically than optically. Whereupon Dr. Boynton set forth his opinions, as above given, with regard to these interesting peculiarities. At the meeting held on the 3rd of last month (March),— Professor S. D. Tillman, presiding, said it would be interesting to resume the discussion of the subject. The fact that the photograph of a lunar eclipse does not correspond with the appearance presented to the eye has been known since the first picture of the moon in partial eclipse was taken in this country. The Chairman having invited Dr. Van der Weyde to give his own explanation, He said, that "if, as Professor Boynton suggested, refraction and dispersion of the actinic rays through our atmosphere was the cause, the reverse should be the case, and the moon should then be obscured less by actinic rays than by the mere visible rays, the actinic rays being more refrangible. The effect of a refracting atmosphere around a planet would be to make the photographic shadow smaller than the visible one, but, the reverse being the case, dispersion consequent on mere refraction would not explain it. The cause is simply the absorption of the actinic absorption depending upon their proximity to the earth's sur rays when passing through our atmosphere, the amount of their surface, so that the shadow of the earth deprived of actinic rays is so much larger than the shadow deprived of the mere luminous rays, corresponding with the density of our atmosphere. In time of exposure is increased with the descent of the sun, and conclusion, every photographer knows in what rapid ratio the the obliquity of its rays, when the consequent passage of them through a more dense atmosphere deprived them of their actinic properties." May not the many failures to produce a true photograph of the moon sometimes be attributable to the above conditions? ments. De la Rue states that, in a recent attempt to photograph the moon, he failed to get a true impression of some important portions of her surface, clearly visible at the time of his experiMay not the truncated appearance of the horns of the crescent moon, as seen by the telescope, just before becoming completely enveloped in the earth's shadow, and the same appearance of the first crescent form that emerges from the shadow, be accounted for by the refraction of the luminous rays? Is it not probable that the moon sometimes, at her full, in passing in the vicinity of the earth's shadow, some portions of her surface are sometimes reflecting luminous without the actinic rays, while at other times some portions of her surface are reflecting actinic without the luminous rays? Is it not possible that even in her deepest eclipse she may be reflecting actinic rays capable of producing chemical changes? If a series of photographs of the moon were taken at intervals of a few seconds, commencing at a short time before her entering the earth's shadow, and continuing until a few seconds after the eclipse had passed, would we not find these photographic pictures show a lack of uniformity in the actinic force reflected from the moon as she passed through different portions of and even beyond the earth's shadow? Why may not a continuous line of impressions be taken during an eclipse, by moving a sensitised plate slowly over the focus of a telescope, thereby measuring the strength of actinic force by the amount of chemical changes produced upon the plate? May not the difficulties attending photographing the moon at her full sometimes arise from her brushing so near the earth's prismatic shadow, so as to reflect refracting rays destitute of actinic power? Do rays of the sun's light, in passing through the equatorial portions of our atmosphere, and reflected to us from the moon, produce effects different from those passing through portions of the polar regions? At the February meeting of the American Institute, which was not so well attended as it should be, Professor Tillman remarked that the refraction of light produced by the earth's atmosphere differs essentially from that occurring when light passes through a glass prism, or a transparent liquid, since the density of air decreases with its altitude. The difference between the luminous and actinic power in the lunar phenomenon in question, he believed to result in part from the action of both the earth and moon upon the highly attenuated fluid which fills the interstellar spaces. Some of thesis advanced by him several years ago, by which he attempted the members present, he thought, would remember the hypoto account for all the effects of light by the undulations of one fluid. According to that view, calorific power is directly, and luminosity is limited to a single octave of undulations, and the actinic power inversely, as the length of the undulations; perception of colour depends, not on the length or amplitude of these undulations, but simply on the ratios of their lengths, or, which is tantamount, the ratios of their several velocities. The earth and moon, as well as every other planet and satellite, produce undulations in the ethereal medium invisible to the human eye, which may exert some influence in the class of phenomena under discussion. This is a deduction from an assumption as yet unproved, and was only mentioned for the purpose of directing thought towards a field almost unexplored. At the same meeting a "Focimeter" was introduced as the invention of Mr. Mason; and Dr. Van der Weyde made some rather lengthy remarks on the optical chafallacy of regarding the Zentmayer lens as really achroracteristics of various lenses, in which he pointed out the matic. Mr. Carey Lea states, as an important fact in connection with the development of dry plates by the alkaline developer, if carbonate of ammonium be applied in a little too strong solution, it will destroy delicate detail previously developed. • See "Chat." Transactions of Societies. NORTH LONDON PHOTOGRAPHIC ASSOCIATION. W. WARWICK KING, ESQ., VICE-PRESIDENT, IN THE CHAIR. A VERY thin attendance, and the absence of a paper, brought about a general conversation, in the course of which Mr. Simpson stated that he had received a communication from Mr. Gaffield, containing a photograph illustrative of that gentle- SOUTH LONDON PHOTOGRAPHIC SOCIETY. these pages; and as Mr. Booty promised to forward us a copy Mr. BLANCHARD exhibited prints from his negatives of monks, printed in carbon and in silver. The general opinion was, that the carbon print was inferior to that in silver, and we think it a correct one. Mr. Blanchard's lens-one of Dallmeyer's-is either not suitable for the work he applies it to, or he does not use it well. Hair should look like hair, but his monks' beards look like anything but hair. As pictures, these photographs possess some very excellent and high-class qualities. A member, whose name we have not the pleasure of knowing, exhibited a collection of prize prints from the Amateur Photographic Association. These were all remarkably good photographs of exceedingly pleasing subjects, and some of them were such specimens of photography as do not often delight us. One of early morning was quite Turnerean in its expression of misty light and dewy freshness, and in another, mountain and river scenery were rendered with a truthfulness and beauty of light and atmosphere which we never before saw in a photograph, either by an amateur or by a professional operator. THIS evening's proceedings were of a very novel and pleasing Mr. WERGE exhibited some Daguerreotype portraits taken Some by Daguerre, one being that of the inventor's wife. specimens of glass positives taken in America were also exhibited by this gentleman. Mr. A. H. WALL described and exhibited some specimens illustrative of experiments in the direction of illustrations for printing with type from blocks photographically produced, which he thought very promising. He also placed before the members a photograph from a negative etched with an etchingpoint as described by Dr. Liesegang (see page 84), and a specimen of printing on Canson's drawing-paper, by M. de Constant, of Lausanne. Mr. SIMPSON rudely contradicted Mr. Wall's description of this photograph. If he will refer to page 84 he will see that, again in error. as in the recent "ninety minutes' exposure" question, he was traits by Hennah-one of which, a child's head, was exquisitely Amongst many other specimens exhibited, were capital pordelicate and refined-portraits by B. J. Edwards, of a very high class, both as pictures and as photographs, some excellent and very artistic heads by Mr. Faulkener, of Bayswater-we should journal-and a gloriously perfect study by Rejlander, a large very much like to engrave some of this artist's posings for this male head in profile, were also exhibited. Mr. ARTHUR BOOTY exhibited some excellent landscape photographs, produced by himself, one of which had so much artistic beauty, that we requested permission to engrave it for Mr. DALLMEYER exhibited a large collection of photographs, was marred by staring inscriptions every one of which in large letters, setting forth the especial merits of the lens by which each was said to be produced, each such lens What would be thought of an exhibition of works of art, in which every painting or piece of sculpture bore, not the modestly inthey originated, but the names of the tradespeople who vend troduced names of the artists from whose intellect and genius paints or marble stuck on in staring and roughly-written capitals, so as to be more conspicuous than the works they defaced. We must confess that when we saw one of Rejlander's should have felt had we found, say, Cockle's antibilious pills most wonderful photographs thus used, we felt much as we advertisement stuck in overpoweringly large letters on a page of Milton or Shakespeare. This is a miserable want of taste, and we hope Mr. Dallmeyer is the only tradesman who which ought to be generally discouraged at all such meetings, practises it. We know no society of artists who would tolerate this, and we think no society of photographers aspiring to be artists should do so; it degrades them as a class, and drives men members of their societies. of refined and cultivated taste from becoming or remaining Mr. SIMPSON called attention to some of the above photographs as illustrative of the great value of Mr. Dallmeyer's new "Rectilinear" lens. Mr. BLANCHARD spoke at some length on the same subject, claiming for the lens the character of being the only one by which certain subjects could be taken. Mr. DALLMEYER endorsed Mr. Blanchard's remarks, but admitted that he could not recommend the use of this lens for any other subject than those spoken of, inasmuch as it was necessarily of so short a focus that it conveyed a very untruthful idea of the things or places it represented. The perspective was excessively abrupt, owing to the lens being too near the plane of delineation, as might be seen by looking at one of the specimens-a view of the Cannon-street Station, in which a short, narrow street was transformed into quite another thing. In conclusion, Mr. Dallmeyer asked Mr. England, as he had used his "Rectilinear" lens, to "oblige" him by speaking as to its advantages. Mr. W. ENGLAND said he had taken some views by this lens which, if he had not possessed it, would have remained untaken; which, judging by the above, would, in our opinion, have been by far the preferable alternative. The CHAIRMAN called attention to a circular inviting photographic contributions to an exhibition in Darwen (see page 123), and stated that residents in London could send works for exhibition to Mr. Charles Green, Middlesex Hospital. The next will be the annual meeting of this society. A If we are to have ventilation in our dark-rooms, it is well for us to have not only good wholesome air, but, as well, air not charged with dust, which most certainly would be the case if brought in from out-of-doors. My plan is to do away with the door of the dark-room, and in its place build up a crooked sort of an entrance, as seen in the cut following. By this simple plan all light is cut off from the entrance, and the room is as well ventilated as need be, without the troubles which are certain to come from the plan first alluded to. You enter at A, and turning to the left, pass through B, and enter at C into the dark-room D. By this simple arrangement you do away with the door, the constant opening and closing of which raises, during a busy day's work, enough dust to produce pinholes ad libitum. To my knowledge, several rooms built after this plan are an unqualified success. If any reader imagines that the light can possibly get into his room, which I do not, then let him make his passage, B, wide enough to put a partition half-way THE reports of societies, &c., occupy so much space this week, that across, said passage, as seen at E and F, and paint the inside of we defer giving a full report of the above society's last meeting an orange or yellow colour. Should light enough to do injury until our next. In the meantime, we may briefly state that Mr. get in after this addition, then blame the writer.-Charles Griggs, of the India Museum, read a short paper on Photo-litho-Wager Hull, in the Philadelphia Photographer. graphy, &c., and gave some practical illustrations of a very interesting character. Mr. M'Lachlan announced, at considerable length, his grand discovery which has so long tantalised the photographic public, the full value claimed for which will, we fear, not be appreciated by our readers. Mr. M'Lachlan is to read a paper going more fully into the subject at the next meeting. It appears from what this gentleman stated, that the greatest source of all photographic mischief was in the use of three acids not working harmoniously when used in the process of preparing, sensitising, and developing the plate. THE PHOTOGRAPHIC SOCIETY. AMONGST artists, nothing is more common than evenings set apart for meetings at each other's studios. No refreshments are provided, and the meetings are, with that exception, just such as "The Camera Club," reported in your pages, seem to be. I am living at Hampstead, and should be glad to know if there are any gentlemen, photographers or artists, in that neighbourhood willing to join me in starting such a studio club. INJURIOUS ACTION OF MOUNTING-BOARDS. W. J. S. SAYS, | It is evident that a waterproof varnish of collodion or gum may, when freshly applied, protect a photograph from the action of destructive vapours, yet at the end of a year be useless for any such purpose. Herein lies the cause of the little practical faith evinced by photographers in the schemes recently brought before, the photographic societies, to try to protect the present prints by means of varnishes.-Mechanics' Magazine. The carbonate of soda toning bath will not give the richest tones; these are only to be got by the use of organic salts in the gold bath.-Carey Lea. Mr. Lake Price has for some years done nothing in photography, but his interest in it reviving, he has been examining his old pictures. He finds that not more than two per cent. have faded, although toned by the old hypo bath ten or twelve years ago. They are as perfect as ever, and very rich and pure in colour. Mr. Price remarks that he relied upon two things-the use of abundance of gold in the first bath, and the use of a second bath of a strong fresh solution of hyposulphite of soda. The latter was very essential. MM. Fordes and Davanne state, with reference to their former remarks concerning photographic mounts with gilt borders (see page 87), to the use of which they traced an injurious effect on the photographs that "M. Jacobo, a photographer of Charleville, made a strong diversion at first from this idea, by sending us cards printed in red, all of which presented the same kind of defect. We could immediately verify that the ink used to make these red impressions contained vermilion or sulphuret of mercury; but, in reality, the ink was not the cause of the spots. They proceededfrom the bronze dust flying about in the atelier and during the printing, or which had adhered to the photographic instruments which had been previously used with wetted and gilded cards; and, in fact, on these red wetted cards we have found defects in the course of formation, in the centre of which small pieces of bronze could be seen with the microscope, which were not yet altered. We have examined a little of the dust gathered in the atelier where these cards were manufactured, and we find it holds an enormous quantity of metallic particles. The last and the best proofs remain. This is to scatter on an image particles of bronze, and examine the effect of it under the action of moisture. Soon the metallic points become altered; it is blackened and surrounded by a golden-white A few weeks ago, we received from Mr. Mann a halo, presenting all the characteristics of the alterations which sample bottle of his negative varnish to test against any have been the subject of our inquiry. The alteration pointed out other varnish we chose to employ. It was tried against explains itself on calling to mind that the photographic image Schnee, and several other commercial samples, the mode of is composed, according to the investigations of MM. Davanne testing being by varnishing different negatives, and placing and Girard, of metallic silver, and, above all, of a combination them out of doors. Within a week the Soehnee showed signs of silver with organic matter, which forms the colouring of the of cracking, and of leaving the film. Mann's varnish has out-proof. This compound is destroyed by the metallic powderlived the whole of the others, and now, after a month, shows but little symptoms of breaking up. Bits of Chat. alloy, the action of which appears to be so much the more rapid and intense the less strong and less washed the proof. We have received from Mr. Griggs, of the India Museum, a magnificent photo-lithograph of a "Delhi embroidered shawl, white silk on black net," and also a superb specimen of photo-chromo lithography, representing the fabric and exact colours of a "Loom-embroidered turban-piece, Hyderabad, Deccan." Nothing could be more perfect or gorgeous than these photographic and coloured representations. Every thread and colour in the texture of the embroidery and cloth is shown with the utmost fidelity, so faithfully indeed, that one would be disposed to believe that a piece of the real article has been pasted down on a sheet of cardboard. These form two of a large series intended to illustrate the great forthcoming national work, by Dr. Forbes Watson, on the textile manufactures of India. At a late meeting of the French Photographic Society, M. Davanne, on the part of M. de Constant-Delessert, communicated the following observations on the dry process, which he has carefully studied:-One of the simplest, in his opinion, and that by which he has obtained the most certain results, is the gum process, in which the collodionised glass is covered with a solution of gum arabic, with the addition of a little sugar. Plates thus prepared keep well, and the results are always good; there is great delicacy obtained, and much rapidity in the operation; the distances present that gradation of tints, and that aërial perspective which the artist should always seek to gain. The coffee process, which M. de Constant-Delessert practised, according to M. Baratti, has, above all others, an exceptional facility of preservation. The plates thus prepared will keep good after two years; and it is this property, without doubt, which has gained that method such preference that it has been adopted by the English in the Abyssinian expedition ; for our operators on the other side of the water never neglect, in their distant expeditions, to obtain a familiar knowledge of new countries through the incontestable fidelity of photographic views. The morphine process of M. Bartholomew has also been the subject of experiments. This mode of preservation is less rapid than the preceding; but there is one marked advantage about it as regards coloured subjects which are scarcely photogenic-it permits, in fact, a very long pose without leaving any trace of over-exposure. The best advertisement for a professional photographer is a good artistic photograph. Meteorological Keport FOR THE WEEK ENDING APRIL 15TH, 1868. Taken by Messrs. Negretti and Zambra with Standard Instruments, at their Establishment, 153, Fleet-street. Observations taken at 10 A.M. The readings of the maximum thermometer and amount of rainfall refer to the day preceding that on which they are tabulated. The fine weather of last week was très à propos, and to many, no doubt, very acceptable at this holiday season of the year, although at the time of writing last week's report it was not to be expected. On the contrary, when the readings of the barometer, &c., &c., were taken as a guide, the wind, instead of remaining southerly, as it had been some days, suddenly veered to the directly opposite quarter, and the effect was soon perceived, driving away all moisture before it. The barometer commenced to rise immediately, and fine weather followed. Notices. TO OUR READERS. THOSE of our friends who may find it more convenient to have THE ILLUSTRATED PHOTOGRAPHER sent by post, can have it POST-FREE, on the following terms, if prepaid; 1 13 52 s. d. week, one copy 0 4 4 4 17 4 " 99 99 8 d. Two copies 07 7 7 30 4 P. O. Orders or stamps to be sent to the Printers, Watson and Hazell, 5, Kirby-street, Hatton-garden, London, E.C. N.B. We have received a number of letters complaining of irregularity in the delivery of our numbers. The fault is not with the publishers but with the agents. THE ILLUSTRATED PHOTOGRAPHER is published at the office regularly by ten o'clock on Friday morning. Subscribers failing to get copies supplied in due time should send their subscription direct as above. OUR SEPARATE ILLUSTRATION.-The issuing of this month's separate illustration on toned paper has been accidentally delayed until our present issue. We hope our readers will overlook the delay. For the future, we shall endeavour, by being beforehand, to avoid such accidents. Mr. Rejlander's works so frequently speak for themselves more eloquently than words can speak for them, that we have omitted the usual descriptive paragraph, To Correspondents, "THE INVENTION OF PHOGOGRAPLY."-This article is again held over through press of matter. TYRO. After many trials, we decidedly disapprove of permanganate of soda or potash for rectifying old negative baths. You had better render it slightly alkaline with ammoni, and sn it for a few days. 2. We do not recommend Albuyou to buy the stock of old albumenised paper because it is cheap menised paper, unless kept in a very dry place, rapidly deteriorates. 3. According to the class of lens you want. A. B. C.-The dictionary is correct, of course. 1863 is correct, not 1813. J. S.-If you are desirous of seeing the advertisement pages you should purchase the journal in numbers instead of parts. We shall adopt your suggestion. Thanks. JOHN GREEN.-M. Salomon's photos are, we believe, mostly whole-plate size. QUERY.-You may use purified methylated ether for your coll dion without any bad effect, but we do not recommend methylated alcohol. 2. For your bromised collodion you may use, say, three grains bromide of ammonium, and five bromide of cadmium to each ounce. Dilute your plain collodion with equal parts of strong ether and alcohol. You have been using too much pyroxyline. J. H. HEARTIE.-1. The colour of the untoned print enclosed is not too red, if your toning bath is in good working order, when the print would come out rich and brilliant. 2. Your silver bath is not too weak for the salting material in the paper. 3. The sensitising bath is not too acid, but should it become so, you can reduce it to neutrality without any evil effect, either by ammonia or bicarbonate of soda. SPE-VIVO.-Your note has puzzled us. Can you send us a sample of the grey metallic powder, which cannot possibly be carbonate of silver, or it would di solve in the nitric acid and water with the utmost facility. If in the neighbourhood of King's College any day in the forenoon, with time to spare, Mr. Dawson would be glad to see you on the subject. OUR "GOSSIPING PHOTOGRAPHER" states that "half an hour" in his article, on page 117, should read "an hour and a halt." X. L., ENT.-1. Add a little pure ether to the collodion until it flows over the plate readily and smoothly. 2. Your room is evidently in a bad situation, and your difficulty arises froin this fact rather than from its peculiar torm, no alteration in which could greatly improve your neg tives. All you can do is to meet the difficulty by its removal to a more suitable locality. If you cannot do this, adopt a collodion bath and developer, which will aid you in securing great contrast and density. 3. If you will refer to our rep rt, on page 134, you will see that we have not let this display or bad taste pass unrebuked. 4. Humbugs and impostors never flourish long after they are really found out, and the persons you name must already be so well known that we need not further expose them. 5. Mr. Sanford would give you the information (see advertisement). The presentation prints for the year at the South London Photographic Society are," Night in Town," by O. G. Rejlander, and "Going to Market," by H. P. Robinson. Y. Z.-The gentleman is an amateur, so that your strictures are quite uncalled for. Y. Z. has not a wise head, or he would not have made such a mistake. DEMOCRITUS.-"Photographers we have known" will probably be com We could not get the drawing graphotyped in time for n enced in our next. this week's number. SOCIAL SAM.-The keeping properties of iodised collodions constantly vary. Some change rapidly, some slowly, some alter most at first, and afterwards change but slowly, others remain long unaltered, but, when the change comes, deteriorate very rapidly. The temperature and other circumstances also influence such changes. You will therefore perceive that we cannot give a satisfactory reply to your question. NOVICE. Allow the plate to remain lorger in the bath, and if you find no This week the barometer is still very high, and the wind remains in the same position with a remarkable persistency; yet, taking general appearances from meteorological data, the expected change must soon follow, and probably in a few days improvement, try another collodion. The wax used is white; hard wax,, not dull weather andrain will take the place of the present weather. bees-wax. Replies to several correspondents are held over for want of space. LONDON, APRIL 24th, 1868. THE MODIFIED GUM PROCESS. BY MAJOR RUSSELL. N the following I give an outline of Mr. Gordon's modified gum process:-Add 2 grs. bromide of cadmium to each ounce of common bromoiodised collodion; excite in a 40-gr. bath not less than ten minutes in summer; wash in two distilled waters, then thoroughly under a tap rinse with distilled water, and flood with a 3-gr. solution of gallic acid; drain slightly, and at once apply a fresh solution of gum and sugar-candy. Develop with pyro, bromide of ammonium, and carbonate of ammonia, applying the pyro and bromide without the ammonia for a few seconds at first. Intensify with pyro, citric acid, and nitrate of silver. Always paint the backs of the plates, With the exception of the large proportion of bromide in the collodion, painting the backs of the glasses, and the alkaline developer, the good effects of which were not then known, this plan is nearly the same as one by which I worked a great deal some ten years ago, and thereby became pretty familiar with the good and bad qualities of gum. Gum and gallic acid plates can be made to give quite as good pictures as any others; the chief difficulties are that the gum causes blistering in development, that it disagrees with developers, acid and alkaline, quickly causing discoloration and turbidity, and that it makes the film very transparent, and so favours violent blurring. The first difficulty is so serious, that I think it a fatal objection to the use of gum; unless a special collodion be used, it is almost impossible to prevent the blistering, so energetic is the action of gum in driving water through the film when moistened; and it is difficult to get a collodion which will be certain to adhere to the glass The second difficulty is probably that which induces Mr. Gordon to apply the soluble bromide at first without the ammonia; this can hardly fail to make a longer exposure necessary. The third difficulty, that of blurring, can now be met in the way directed-thanks to Mr. Marlow's important discovery of the cause of the fault. It is difficult to understand why the gallic acid is directed to be applied separately; it is a better and simpler plan to use it dissolved with the gum, for in this way the gallic acid is certain to be evenly distributed-a point of much importance. The same mistake was made some time back in an attempt to revive the use of gelatine and gallic acid. My experience with gallic acid on dry plates began a few weeks after the first publication of Taupenôt's process; the gallic acid was at first applied to the collodio-albumen plates, after slight washing in distilled water; development was facilitated, but it was not easy to avoid stains, and the plates would not keep. The plates were, therefore, before using the gallic acid, soaked in common water, and soon afterwards the plan was adopted of treating with solution of common salt, and then washing for half an hour. The same treatment was subsequently applied to plates prepared with gelatine, or metagelatine, and with gum; gallic acid being mixed with the "preservatives." It was the superiority of tannin over gallic acid, when the former was substituted for the latter in mixture with gum, which gave me the first idea of the value of tannin in photography. There is no reason for using fresh gum; it can be preserved by oil of cloves, or otherwise; the gum and gallic acid may be kept and used over and over again indefinitely. Mr. Gordon says that he does not like to remove the nitrate of silver chemically, and that salt and bromide make the negative less bright, and impair the keeping. These things seem to be mistakes, as the plates prepared by Mr. Gordon's method will keep for months in summer. The silver must, I think, be removed chemically, for it is contrary to all experience, that plates on which nitrate of silver Vol. I.-No. 12. and gallic acid remain, could possibly keep long. Common bromo-iodised collodion, with the addition of grs. to the ounce of bromide of cadmium, will, after ten minutes in a 40-gr. bath, retain a quantity of unconverted bromide amply sufficient to remove all traces of nitrate of silver chemically, when washed out by a few changes of distilled water. The salts in common water greatly accelerate the removal of the nitrate of silver. The mischief to be feared is, that people, fancying that a trace of nitrate of silver should be left on their films, may wash so slightly as sometimes really to leave some. The utter uncertainty and dismal failures which often result from such treatment, ought in time to teach the lesson, in perhaps the most satisfactory way, that no trace of nitrate of silver should ever be left on a dry plate. The bad effect of a slight t:ace of the nitrate will be most marked when gallic acid or tannin is used in the preparation, in hot weather, or after long keeping. Soluble iodides haye a very mischievous effect, when not removed, as they are not easily, by washing; but I never could find that bromides or chlorides did any harm after being thoroughly washed out again. A plate which had been steeped in a 40-gr. solution of bromide, has, in my hands, after some hours' washing, worked perfectly well. Any harm done by bromides and chlorides, probably arises from not again removing them. Not long ago I knew of an instance of a collodio-albumen plate giving a good negative after it had been kept seven years. This plate had, in the preparation, been treated with salt, well washed, and finished with gallic acid. This does not look as if salt impaired the keeping quality. To set against the great disadvantage of blistering, gum probably has one solitary advantage, under some circumstances, over tannin. Gum plates are less likely to suffer from the presence of alkaline matter or carbonates, in the water used in the preparation. Too little attention has been given to this difficulty with tannin. It is really no difficulty at all when understood, as will be explained in a future communication. In a letter just received. Mr. Griffiths tells me that he had already found out and put in practice some of the improvements described by me in the last number of this journal, and also another alteration in working, which I have lately made, but not yet published. It is very satisfactory to have one's own experience confirmed independently by so intelligent, careful, and successful a worker as Mr. Griffiths. THE DARWEN EXHIBITION. A PARAGRAPH has already appeared in THE ILLUSTRATED PHOTOGRAPHER, announcing an "exhibition of art, manufactures," &c., at Darwen, Lancashire, for a charitable object. Till within the last few days we were not aware of the whole scope and object of the promoters. It is "to provide funds for the completion of a building, now in progress, intended as an educational institution in a part of Darwen where it is greatly needed. Beyond this the committee desire to serve a wide and scarcely less important purpose-the elevation of the artistic taste of a large and increasing population, in a district where no such exhibition has ever before been attempted." The names of the patrons and of the committee include those of several well-known noblemen, twelve members of Parliament, besides a large number of men well known in the industrial and art records of our country. The room in which the exhibition will be held is thirty feet long by ninety feet wide, and has been divided into courts for the classification of the various works of art exhibited. The photographic department will be forty-four feet by thirty feet. We are appealed to, specially in letters from the manager, to help them in getting up the photographic department to a proper standard of excellence. The expenses of carriage to and from Darwen, of all packages, are guaranteed |