stop in. The marginal rays strike its surface and are prevented from passing through the lens. The central rays alone pass through and give a clear image with no "splashing" around the edges.

Stops have another value in correcting vignetting—the distribution of more light in the center of the plate than in the corners. There are two reasons for this action. In the first place, rays coming to the center of the plate hit practically at a right angle. They therefore penetrate more deeply into the emulsion of the plate than do the corner rays which hit it at an oblique angle. In the second place, a greater number of rays does actually come to the center of the plate than is received at the corners. We have noticed in focusing that the ground glass is splendidly illuminated in the center but quite poorly at the corners. Remove the ground glass from your camera and look at the lens from a corner of the back of the camera. You will notice that only about half of the lens is visible and that the other half is shut off by the conformation of the lens barrel. Theoretically this would mean that half the rays were excluded from the corners of the plate; but some of them are reflected and we do not lose the entire amount. Now if we put in a stop small enough to be seen at its full diameter from every part of the focusing screen or camera back, it is evident that we get a uniform number of rays to all parts of the plate. Besides this we have cut out the marginal rays and thus improved the definition of the image.

It must be pointed out, however, that we cannot always afford the loss of light that the use of a stop entails. If we divide the lens into three zones, central, intermediate and marginal, each having the same diameter, they will respectively have an illuminating power that can be expressed in a ratio as I to 6 to 15. Therefore when we stop the marginal rays by the use of a stop we do so at a cost of 15 units of light and have sacrificed two-thirds of our illumination.

M

PHOTOGRAPHY AT SEA.

By ROBERT E. M. BAIN.

ANY persons refrain from picture-making at sea from fear that unless a small hand camera be used the vibration caused by the machinery will prevent sharpness of image. The best pictures are always obtained by use of the tripod or stand and the larger cameras can only be used by its means. The vibration in stateroom, engine room and on deck, especially on the fast steamers, is very noticeable, but a little thought will prove that the camera vibrates in common with its surroundings-not more so-hence timed exposure may be made with impunity even for an extended period of an hour or more, with the best of results. Many interior views may be made by placing the camera in a steady position, anchored as it were and left for a long period without further attention, and the results found as good as if taken ashore under the best circumstances.

Plates and filters are now supplied which are sensitive to color value and these are most desirable in "seascape" work in view of their adaptability for cloud effects-most necessary in such pictures. Even for views on deck and in the saloon the color value is a feature, for the yellow-brown of the planking and the color scheme of the decorations are quite flat otherwise.

As a hint at desirable subjects to be found at sea we may mention the forward deck, particularly when the seamen are belaying or getting ready to drop the big anchor. The companionway to the bridge generally shows a quartermaster on duty, an excellent subject. A little persuasion will induce a good humored officer to pose either "on deck" or on the bridge. The wake of the vessel is always a favorite, and since it is not necessary to have the camera vertical the effect of the tumbling water is very attractive. On some ships the "fire drill" and the "boat drill" make interesting pictures, but this work at practice drill is generally performed now-a-days in port. With the use of the tripod a most interesting picture may be made when the vessel is "signalling" at night to a passing ship. It would be impossible to hold the camera in the hand steady enough as the exposure should last the entire time of the burning of the Coston light to get the best effect. Many interesting pictures can be secured of the steerage passengers dancing and singing. If the weather is fair and the ship fairly steady a curious picture may be obtained of the deck by hoisting the camera by the signal halliards, lens down, and snapping the shutter by means of a cord. The "taking" and "dropping" the pilot are always subjects of interest but not to the same extent as when the small pilot boat met the ship "600 miles out." The steam pilot boat has spoiled much of the romance of the pilot's coming aboard. Coming into and leaving port afford excellent means of obtaining interesting views, not the least of which is the crowd on the dock or pier. The arrival of the doctor's boat at Quarantine, with the Government reservation as a background, is attractive as a picture; and the run down the harbor of New York requires mention as among the list of interesting subjects. Bear one thing in mind, however, it will be useless to ask permission to take views from the bridge and the suggestion will hardly be received with favor.