London: C. J. CLAY AND SONS, CAMBRIDGE UNIVERSITY PRESS WAREHOUSE, AVE MARIA LANE. Cambridge: DEIGHTON, BELL AND CO. Leipzig: F. A. BROCKHAUS. FELLOW OF TRINITY COLLEGE, CAMBRIDGE; PROFESSOR OF MATHEMATICS IN THE MASON COLLEGE, BIRMINGHAM. Cambridge: AT THE UNIVERSITY PRESS 1888 [All Rights reserved.] Geft 4-12-33 PREFACE. THE present work is essentially an abridgment of my larger treatise on Geometrical Optics, and is primarily intended for the use of students who require an exposition of the principles of Optics and their application in the use and construction of optical instruments, without very extended and complicated mathematical analysis. It is elementary, inasmuch as it uses no mathematics beyond trigonometry. In the task of selection and arrangement, I have departed somewhat from the traditions of previous writers of elementary text-books on Optics. My object has been to include only those parts of the theory which could be investigated completely and satisfactorily by elementary methods, and to treat those parts as fully as possible. Thus, while giving an account of the method of correcting optical instruments for their most important defect, that due to chromatic dispersion, I have omitted entirely the theories of aberration and of thin pencils, believing that they are not suited to elementary treatment and that they should be postponed until they can be investigated by more advanced and comprehensive methods. On the other hand the theory of lenses, as developed by Gauss, has |