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THE PHOTOGRAPHIC NEWS. LAPRIL 24, 1885. coarseness according to the length of exposure; this goes so far that the images of two thick Jines or points standing close together (within certain limits) will finally join. This effect will be more readily produced if the covered spaces which should remain white allow some action of light to take place through them under long exposure. If we expose a network of fine lines at a distance apart of about sb of an inch to diffused light under a sensilive plate, and cover it over in slips, so that the first slip shall have a normalexposure, and the remainder be over-exposed from twice to four times, it will be found that the first slip will correspond with the original, while the rest will show distinctly thicker and thicker lines, till finally they join together. The same effect occurs when the lines are exposed under a half-tone negative. In the clear parts the lines will be found closed up after a sufficient exposure, and will gradually open out until finally those under the densest parts (the lightest half tones) appear in their proper dimensions. To produce the proper effect, therefore, the exposure must be prolonged until the lines or points which represent the finest tones in the lights are sufficiently clearly developed. (To be continued.') AN ATTEMPT TO PHOTOGRAPH THE CORONA. BY W. H. PICKERING. It occurred to the writer that the late partial solar eclipse would be an excellent chance to repeal Huggin’s experiments on photo graphing the corona. A 3-inch refractor of about 40 inches focal length was employed. A drop-shutter was attached to the lens, giving an exposure which was estimated at about a fifth of a second. A piece of deep-violet glass was procured, which could be inserted just in front of the plate, or removed, at pleasure. By its use a negative image of the sun's disc was ob tained, but without it the plate gave a reversed image ; the sun being a positive and transparent, while the surroundings re- mained negative and were dark, the appearance being strikingly similar to that of a photograph of a total solar eclipse. Both bromide and chloride plates were provided ; but, as with Mr. Huggins, the latter proved proved to give much the better coronal effects. A ferrous-oxalate developer was employed, which contained a large proportion of potassium bromide. The weather throughout the eclipse was wholly favourable; and we began photographing at ten o’clock, two hours and twenty minutes before the eclipse began, and continued at work until five minutes past four, or an hour and ten minutes after it had terminated. Photographs were taken every half-hour, with extra ones interpolated ar the more interesting phases, making twenty-nine pictures in all. Very corona-like effects were certainly produced, faint rays here and there shooting out perpendicularly to the sun’s surface. But, unfortunately, no two of the pictures were alike, and the corona in front of the moon was quite as well marked as that on the other side of the sun. Indeed, the most corona-like ray produced, appeared in one photograph stretching directly to wards, and terminating at, the centre of the moon. Nine photo graphs taken in succession showed one side of the halo stretch ing to a greater distance than the other ; but in one of these the darkening was carried so far out, that it became nearly separated from the rest of the corona, and appeared as a distinct dark circle of the same size as, and by the side of, the image of the sun. This, of course, showed it to be merely an internal reflection of that image, and nothing more. During the course of the experiments, the object-glass was revolved about its optical axis, photographs being taken in four positions. No effect, however, was discernible upon the plates. The conclusions I should draw from my experiment are 1st, that, though it is very easy to obtain a corona-like image, one may readily be deceived in such matters, and the same effect be obtained by our atmosphere, without the aid of the solar corona, combined with little defects in the gelatine film (this, I think, is conclusively shown by the extension of the pseudo-corona in front of the moon) ; 2nd, that chloride plates are more suitable than bromide for obtaining an atmospheric corona, just as Mr. Huggins has claimed that they are more suitable for taking a solar one ; hence I think one must not rely too much on the ultra-violet region sensitiveness of the chloride plate for a sepa ration of the two ; lastly, though my experiments fail to cor roborate Mr. Huggins’s results, they do not, of course, show that his corona may not be solar, but merely indicate that under very favourable circumstances I could obtain no trace of it. I h ive before me a print made from a negative by Dr. 0. Lohse, in October, 1878, showing effects very similar to those obtained by myself, except that his view was not taken during an eclipse. He considers that the halo is wholly atmospheric, and not coronal. MOUNTING LARGE PHOTOGRAPHS. BY F. J. HAYNES. HAVING recently had a varied experience in mounting full sheet prints, I would be pleased to inform your numerous readers of our method of mounting and preventing warping, if the follow ing is of sufficient importance to justify its publication. If mounting on cardboard 22 by 20, have a stretcher made of 3-inch strips well put together, 23 by 27 outside measure ; this allows half-an-inch margin over the cardboard; mount the print as usual on the dry cardboard, place it face down on the stretcher, and cover the back with a piece of strong Manilla paper large enough to bind the print and cardboard securely to the stretcher. Allow it to remain on the stretcher until tho roughly dry. If your back paper is poor, the contraction will break it loose from the stretcher, and the desired effect will not be obtained. But if a first quality of paper is used it will hold it securely ; and when the cardboard is cut loose, it will be as straight as the original cardboard, and will remain so. Large views mounted in this way can be placed in portfolios on easels, &c., with some pleasure ; they will not be like a lot of stove pipes. We have mounted during the last three months some two thousand, and can recommend this plan as entirely satisfactory, and certainly one that is appreciated by the purchaser of the views. Any number of these stretchers can be made; but with twelve we have been able to get along rapidly enough, as the print dries in a few hours, when it can be cut off, and the stretcher is ready for use again.—Photographic Times. orrespondence. THE NEW DANGER. Sir,—The subjoined extracts from correspondents will prove the interest taken by the profession in the above case. As the matter is still in the hands of my solicitor, I refrain from making any remarks.—Yours truly, 49, King William Street, E.C. A. L. Henderson. A Northampton photographer writes : — “ Dear Sib,—I have just returned from a short holiday, and on picking up my News found your letter, ‘ A New Danger.’ I must confess to feelings of thankfulness that you bad the promptitude to unmask the wretched cheat. I have no clubs here, so naturally I was pleased to read your letter. I knew that the individual, on being liberated from prison, was going on for a London firm ; bnt I little thought he had ventured to use your name. I am afraid I can be of little service, but please com mand me if necessary in this matter.” “Dear Sir,—Seeing a letter in the Photographic News of last week of yours, 1 beg respectfully to call your attention to what I think you may, perhaps, have overlooked in connection with the 1 New Danger.’ First, your letter would only be seen by at most about sixty or seventy persons, as not more than that number of copies of the News are circulated in the town. Second, as your letter does not mention the name of the canvasser re ferred to, it throws discredit upon all canvassers in this town. Knowing you have for many years past exposed various shams and frauds in connection with the profession, I feel sure you would not willingly wish to brand all for one. I would suggest that if action be not taken before the magistrates, that an ad vertisement in the Northampton Daily Deporter or Daily Chronicle disclaiming your connection with the so-called firm would at once set the matter at rest. I trust you will pardon the liberty I am taking in this matter, but I am speaking on