_Apparatus and chemicals for development._—The development of the plates or films after exposure in the camera requires practice and experience in order to secure the best results. Instructions for development are sent out with all commercial plates or papers, but many failures would certainly result from attempting to work by these without some preliminary practice at home. As plates, &c., will keep after exposure (if well protected from damp) for 18 months, or longer if properly packed, it is not, of course, necessary to develop them _en route_, although if the traveller possess sufficient skill, and if ample water-supply and other facilities can be secured, it will be advantageous for many reasons to do so. On a long journey, when the temperature is not too high, use of convenient resting-places may be made to develop from time to time a few plates selected from the whole, both as tests for exposure and as proof that all the apparatus is in order. The following list comprises all that is absolutely required for developing 8 or 10 dozen gelatine plates:—Three papier-mâché dishes, two 3-ounce glass measures, three 6-ounce bottles, containing strong solutions of pyrogallic acid preserved with potassium meta-bisulphite, potassium bromide, and sodium carbonate respectively, 1 lb. hyposulphite of soda, and ¼ lb. alum, both in crystals, 4 or 5 feet of india-rubber tubing and a spring clip, to make a syphon for a water supply from a jug or can, a basin or tub to serve as a sink, a folding rack for draining the plates. There are several convenient new developing agents in the market: Hydro-Kinone, Eikonogen, Glycin, Metol, Rodinal, and Amidol. Some of these were made and named in Germany, they are no longer procurable under their German names. English manufacturers are however making substitutes quite as good under new names, and these can be obtained from the dealers. Many of them can be obtained in compressed form. The traveller is recommended for advanced study of photography, such works as Instructions in Photography by Sir Wm. Abney, The Science and Art of Photography by Chapman Jones, and The Manual of Photographic Exposure and Development by Alfred Watkins, which may be had from any photographic dealer’s. The aim of the traveller-photographer should be the production of good _negatives_. It often requires years of study on the part of professional operators (with advantages impossible to the traveller) before thoroughly good negatives are habitually produced; and it must not be supposed that a person taking up photography for the first time, in a few hurried moments before departure on a journey, will attain other than very unsatisfactory results.