PREFACE. THE nomenclature of a science is one of the most im- portant portions of its structure, and the Science of Instruments requires a good dictionary as a basis. It is believed that a concise definition of each instrument, together with illustrations of the most important types, will be of real service to scientific men and the industry. This book is not only a means of information and reference respecting scientific instruments of every description, but also exhibits the great variety of such instruments that are produced in Great Britain. Key numbers corresponding with a numbered list of manufacturers are attached to the dictionary descriptions. The British Optical Instrument Manufacturers Association, under whose auspices the book is issued, is composed of the leading Optical Instrument Manufacturers of Great Britain, the names of whom will be familiar throughout the world. From these houses have emanated in years gone by the original types of which the presentday highly...