The camera looks rather complicated, but it is really simple. Its body consists of front and back, each attached to a central part by a short bellows and sliding on a base board, to which it can be clamped by screws of the usual pattern. The central part carries trunnions, such as are used for looking-glasses, which swing in sockets carried by two upright supports, so as to give the whole free motion in a vertical plane. In order to be able to fix it firmly at any angle, the base board of the camera body carries on its underside a thin board projecting beneath it and forming a segment of a circle whose centre would be the horizontal axis through the trunnions. The board passes between the jaws of a small wooden clamping vice in front, which is carried by the square base to which the uprights are fixed. The whole is firmly made of well-seasoned pine, and has stood well the hard usage of half a dozen years. There is no focusing screen. Focusing was done with great care once for all, and then a coat of hard varnish was put over all the adjusting screws. A small view-finder is attached to one side, and it was by this that the camera was pointed in the desired direction. In order to lessen risk of mistake, it was so arranged that the two slides belonging to one camera would not fit the other. The lenses, of 18 inches focus, and giving sharp detail all over the plate, were carefully matched, and the focus adjusted until the images given by them when placed side by side appeared to coincide exactly. They were provided with iris diaphragms, which were shut down to an aperture of a quarter of an inch, and with shutters which could be released at the same moment by an electric current, acting through the electro-magnet shown under the lens on the front of the camera. The shutters were of the kind known as the “Chronolux,” which will give any exposure from the sixty-fourth of a second up to three seconds. But it was found in practice that the highest speed was sufficient and gave satisfactory results. Of course, there was no idea of adjusting matters on each occasion so as to get the best possible negatives capable of yielding good prints. Measurement was the object, and if the negative showed the sun and sufficient cloud detail for the identification of cloud points, that was all that was wanted. The shutters gave a good deal of trouble at first. Their sliding parts were made of ebonite, and when the cameras were left in their stands with an August sun shining down upon them, everything inside got very hot and the ebonite warped; but the difficulty was got over by substituting aluminium.