Having thus briefly considered the essentials for a hand camera, it only remains for us to give one or two general hints which may be of service. First, as to the plates to be used for ordinary instantaneous work, we undoubtedly recommend the most rapid that can be obtained, those marking 24 or 25 on Warnerke's Sensitometer; but at the same time one or two plates of a lower degree of rapidity should also be carried for time exposures. Secondly, as to the size, the most convenient will be found the quarter-plate or 4¼ by 3¼ins., as from this size lantern slides may easily be made by contact printing, or they lend themselves equally well for the purpose of enlargement. Thirdly, as to the development of the plates. Rapid plates are most difficult of all to develope successfully, even when they have received time exposure of from ¼sec. and upwards, but when only the fractional part of a second, such as 1/100, 1/50 and so on have been given, then the successful development is a feat to be proud of. The method we strongly recommend is to soak the plate first of all in the alkali or accelerator, either ammonia p. 21; soda, p. 77; or potash, p. 17; then add after about one minute's soaking, ¼ grain of pyro or hydroquinone, and allow all detail to appear, then add more pyro or hydroquinone to allow the required density to be gained; in fact a very good plan, which originated we believe in America, is to soak the plate first of all in the accelerator and then transfer to the pyro or hydroquinone, allowing only the accelerator absorbed by the film to enter the second bath. This will usually be found sufficient, but if not, a slight addition of alkali to the pyro or hydroquinone will give the required density.

The Detective or hand camera shown in p. 113 is one which will be found to answer most effectively every requirement of the practical worker in this branch. A neat black leather covered box, 9¼ by 5½ by 7½ins., unsuspicious in character, encloses a camera, with space for six double-dark slides (three only being sent out with the camera), a sectional view of the same is given in p. 113; the other diagram gives a general idea of the external appearance and likewise gives the arrangements of its working parts. A sliding panel covers the lens when not in use, and an Euryscope, Rapid Rectilinear, or Rapid View Lens is supplied according to the length of the purchaser's purse. The shutter is so arranged that time or instaneous exposures may be given, the fastest being about the 1/100 sec. The diaphragms are inserted in the lens tube in the usual manner upon opening the lid of the box. The dark slides are of specially light form, and the shutters pull right out, and the slides being much cheaper than the ordinary ones, allow more to be obtained without inordinate outlay. Two Finders are also fitted, which show the subject included on the plate when it is either vertical or horizontal; and a screw hole in the base enables it to be used upon a stand if desired.