While the advantages of automatic cameras are great it must not be overlooked that a camera which can only be operated automatically is of limited usefulness. It is not suited for “spotting” at any definite instant, as, for illustration, at the moment of explosion of a bomb. It should, therefore, be the aim of the automatic camera designer to so build the apparatus that it can, at will, be used semi-automatically. In addition, to meet the contingency of any break-down in the source of power, the camera should be capable of hand operation, as in the case of the American semi-automatic deRam. In short, the automatic camera should not be a separate and different type; it should merely have an additional method of operation. Certain desirable mechanical features of all aerial cameras have already been enumerated. Some of these may be repeated here with the addition of others peculiar to automatic cameras. As a general caution, mechanical motions depending on gravity or on springs should be avoided. Movements adversely affected by low temperatures (20 to 30 degrees below zero, Centigrade), are unsuitable. All adjustments called for in the air must be operable by distance controls whose parts are large, rugged, and not dependent on sound or delicate touch for their correct setting. The center of gravity of the camera should not change during operation (important in connection with the problem of suspension). The camera should work in the oblique as well as in the vertical position. The power required for operation must not exceed that available on the plane. Electrical apparatus, for instance, should not demand more than 100 watts. Any devices which diminish the weight of the camera are particularly desirable in automatic plate cameras, because of the large number of exposures which such cameras encourage. For instance, if the plates could be handled without placing them in metal sheaths we should gain a substantial reduction in weight (the sheaths weigh nearly as much as the plates) as well as in the time necessary for handling. =The Brock Automatic Plate Camera.=—This camera is somewhat similar to the same designer's film camera, both in shape, in size, and in its employment of a heavy spring motor for the driving power. It uses 4 × 5 inch plates, and carries a 10 to 12 inch lens.