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containing box is of such a size as to admit the cylinder and regulator without leaving any room to spare, ex cept half an inch clear above the top of the regulator, as shown in the annexed diagram. To prevent the cylinder shifting upwards, two strong posts are affixed to the internal sides of the box, and these just catch the shoulders of the gas vessel and keep it firmly in its place. These posts, marked PP in the illustration, have a farther use. When it is desired to attach a gauge to the cylinder for the purpose of ascertaining the quantity of gas available, the vessel must be re moved from its box and the regulator detached. This can easily be done by lifting the cylinder clear of the posts PP, and pulling it forward in the direction of its head. It can then be allowed to rest on the projec tions PP, and will be held firmly there by its own weight while the necessary adjustments are being made. The black rectangular marks sho wn on each side of the open box are T-shaped clamps which are screwed firmly in place, and which permit the lid of the box BB to slide beneath them. It will be observed that the lid has three openings cut in one of its edges. These have the same distance between them as the clamps J, so that when these openings come opposite to the clamps, the lid can be removed without sliding it the whole length of the box. When this lid is wholly closed over the box, it is secured for travelling by a cheese-headed screw S, which is received into a plate provided for it at the end of the box. The india-rubber tube for attaching the cylinder to the lantern is a fix ture on the regulator (not shown in the diagram). It is about eight feet in length, and conveniently lies along the edges of the cylinder, down one side and up the other. The only other feature of this box which need be mentioned is a simple but very necessary one, namely, the presence of a strong wrought iron handle at each end—something that the hand can grasp well, and that will resist a good deal of knocking about. It is the fashion generally to tie the cylinder or cylinders to the leg of a table, so that the regulator is upright. There is no nec.c.ity for this, as the appa ratus works quite as well when lying on its side. It is in this latter position that wc use it, for the boxes containing the cylinders lie side by side on the floor, between the legs which support the lantern-box and lantern. All that the operator has then to do is to remove the securing screws from the lids, slide the lids a few inches down the boxes to expose the regulators, take out the india-rubber tubes, and make connection with the lantern. It may be added, in conclusion, that there is plenty of room in the boxes, round about the regulators and above the shoulder-pieces of the cylinders, to accom modate the key, spanner, and other things that may be required in dealing with the gases. These are best carried in cloth bags so that they cannot get loose in transit. We also make it a practice to carry a couple of screw-nozzles to fit the cylinders in case an accident should happen to the regulators. These, happily, we have never yet had occasion to employ. ON THE USE OF SMALL STOPS. BY W. H. WHEELER. It has been the fashion, particularly among artists, to deprecate what they considered to be the abuse of small stops. One gentleman, I remember, recommended us all, in the interests of art, to “throw away our wide-angle lenses, and burn all our small stops.” The intention of this heroic advice was excellent. The author of it attributed faults in the perspective of form to the use of wide-angle lenses, and deficiency of atmosphere to that of small stops. No fault need be found with his criticism of results, but his judgment as to causes, and advice as to means, is quite another thing. This is properly our province, and my object in the present paper is to inquire, as thoroughly as I am able, into the advantages and draw backs attending the use of small stops. They certainly require special care in keeping stray light from the camera, because the longer the exposure, the longer does this stray light act on the plate ; but then, cameras should always be light-tight. Again, some workers are slow to realise the rapid ratio at which a proper exposure increases as the stop is reduced, and an under-exposure, with its accompanying want of atmosphere, has thus come to be naturally associated with a small stop. The associa tion, however, is not a necessary one; all plates need a sufficient exposure, if breadth and atmosphere arc desired. But when a sufficient exposure is given, and when stray light is so carefully shielded from the lens and kept out of the camera that this full exposure does not fog the delicate detail which should be perceptible in the shadows —though not too obvious—then, especially when a large scale is attempted, these much-maligned small stops may be found to be the very life of the art of depicting, in all its native delicacy and profusion of detail, nature in repose. We will first inquire, what is the optical aspect of the question ? Those who, accustomed to the use of telescopes or microscopes—especially the former — have learned to appreciate thoroughly the advantages of aperture in their object-lenses, and perhaps unlearned much of their primitive faith in high magnifying powers, have yet a new lesson before them when they turn their attention to the work of photographic lenses. Oblique errors acquire here a new importance, and the novel power of compen sating for reduced light by increased exposure is not at first realised. Neither do we at once appreciate the fact that our accustomed visual power of better distinguishing in the telescope—though only by glimpses—well illuminated details amidst surrounding haze of atmospheric fluctuation, or even of optical short-comings, than when that detail has been dimmed in clearing the haze by reducing the aperture, is not shared by the photographic image. For this is impressed, not by glimpses, but by a steady gaze ; and, after being formed in the negative, it has still to be printed. A similar difference may be observed between an original photograph and a copy ; for the soft haze of indistinct definition, or of slight movement—perhaps that of a near branch out of focus—detracts sensibly less from the charm of an original photograph than when that is further hardened and made more coarse by reproduction. The effect of small stops on a photograph has thus com parative advantages not shared by the optical image when viewed directly through an eye-piece. The appearance of the latter when a large stop is used is much more distinct, as well as more brilliant, than in the resulting photograph, whereas with a small stop it does not equally mislead.
