Transcriber’s Note In what follows, italic text is denoted by _underscores_ while bold text is denoted by =equal signs=. Small capitals in the original text have been transcribed as ALL CAPITALS. Superscripted text is prefixed by the ‘^’ symbol. Braces ‘{}’ may enclose the text when necessary to avoid ambiguity. Subscripted text is always enclosed in braces ‘{}’ but will not be preceded by a ‘^’. ————— See the end of this document for details of corrections and other changes. ————————————————— Start of Book ————————————————— [Illustration: A CHRISTMAS LECTURE AT THE ROYAL INSTITUTION: “WAVES AND RIPPLES IN THE AIR.” FIG. 46 (_see p. 109_). _Drawn by F. C. Dickinson._] [_From the “Graphic.”_ ] WAVES AND RIPPLES IN WATER, AIR, AND ÆTHER BEING A COURSE OF CHRISTMAS LECTURES DELIVERED AT THE ROYAL INSTITUTION OF GREAT BRITAIN BY J. A. FLEMING, M.A., D.Sc., F.R.S. M. INST. E.E., M.R.I., ETC., ETC. PROFESSOR OF ELECTRICAL ENGINEERING IN UNIVERSITY COLLEGE, LONDON _SECOND ISSUE, REVISED_ LONDON SOCIETY FOR PROMOTING CHRISTIAN KNOWLEDGE NORTHUMBERLAND AVENUE, W.C. 43, QUEEN VICTORIA STREET, E.C. BRIGHTON: 129, NORTH STREET NEW YORK: E. S. GORHAM 1912 [PUBLISHED UNDER THE DIRECTION OF THE GENERAL LITERATURE COMMITTEE] PRINTED BY WILLIAM CLOWES AND SONS, LIMITED, LONDON AND BECCLES. PREFACE.