The dictionary of photography: for the amateur and professional photographer (7th edition)

The present edition contains about one hundred and fifty pages of new matter, and three hundred fresh headings ; also between twenty and thirty new diagrams these additions being necessitated by the rapid advance of photographic technics. Notwithstanding these considerable additions, the bulk of the volume has not been considerably increased, as much overlapping matter-or partially overlapping matter -has been eliminated; and this without disadvantage to the reader, as cross-references have been inserted where required. The Appendix, which, in the sixth edition, formed nearly one-third of the whole book, has been incorporated with the alphabetical portion-a change which will facilitate reference, as it brings all matter into one sequence. The omission of metric equivalents from the formula! may appear at first sight to be an undesirable retrogression; but, if so, it is a retrogression which will make the book more convenient for that very large majority who only use the British weights and measures ; an additional column of figures not unfrequently leading to confusion and error. Those who prefer to use the metric system in compounding their photographic preparations, will probably rather gain than lose by the change, as the tables given in the article weighing and measuring will enable them to effect the necessary conversions with any required degree of accuracy. In giving equivalents of the English weights and measures according to the metric system, very inconvenient quantities, expressed by many figures, are generally necessary if exact equivalence or strict proportion is to be secured ; while, on the other hand, the giving of approximate figures may be adopted for the sake of. simplicity of expression. Each course is about equally undesirable, and liable to cause inconvenience. In very few cases, where work of considerable delicacy is involved, and the original instructions were given according to the metric system (e.g., in case of emulsion for the Lippmann process), the original figures have been retained. THOMAS BOLAS