Light And Electricity

LIGHT AND ELECTRICITY IsTOTES TWO COURSES OF LECTURES ZEFORE THS ROYAL INSTITUTION Of GREAT BRITAIN. JOHN TTNDALL, LL. D., F. E. S., AUTHOR OF IIEAT AS A MODE OF MOTION, IEOHTBES ON BOTOTO, FEAQMENOS Off BOIBNOl POK UNSOnSNTIFtO raOPLB, nOTJES OP EXEKOIBB US THE AT, T B, ETC., ETC PHOKE330E OF HAHTEAI. PHILOSOPHY IS TUB noYAL iNSniiraiON OF QEEAT IsTEW TOEK D. APPLETON AND COMPANY, B49 BB1 BROADWAY. PREFACE TO THE AMERICAN EDITION. FOE the benefit of those who attended his lectures on Light and Electricity at the Royal Institution, Prof. Tyndall prepared with much care a series of Notes, sum ming up briefly and clearly the leading facts and princi ples of these sciences. The Notes proved so serviceable to those for - whom they were designed, that they were widely sought by students and teachers, and Prof. Tyndall accordingly had them reprinted in two small books. Under the conviction that they will be equally appreciated by instructors and learners in this country, they are here combined and republishecl in a single volume. No intelligent teacher or earnest student needs to be reminded of the importance of repetition and recapitula tion to give permanence to mental impressions. But it is neither possible nor desirable to retain in the memory the copions details which may be necessary to the first comprehension of a subject. Hence, after listening to a course of lectures, or going through an extended work in which facts, experimental proofs, and speculations, have 4 PREFACE TO THE AMERICAN EDITION. been elaborately presented, it Is invaluable to retraverse tlie field, concentrating attention upon the prominent and established principles of the subject. This is an in dispensable conditionof all solid acquisition and, in thus clearly and sharply stating the fundamental principles of Electrical and Optical Science, Prof. Tyndall has earned the cordial thanks of all interested in education, NETW YORK, April, 1871. PAGE General Considerations. Rectilinear Propagation of Light . . 11 Formation of Images through Small Apertures ... 12 Shadows . ....... 13 Enfeeblement of Light by Distance Law of Inverse Squares . 15 Photometry, or the Measurement of Light . . .,16 Brightness ....... 17 Light requires Tune to pass through Space . . . .19 Aberration of Light ...... 20 Reflection, of Light Catoptrics Plane Mirrors . . .22 Verification of the Law of Reflection .... 22 Reflection, from Curved Surfaces Concave Mirrors . . . .27 Caustics by Reflection Catacaustics . . . . 31 Convex Mirrors . . . . . . .82 Refraction of Light Dioptrics . 33 Opacity of Transparent Mixtures . . . . .39 Total Reflection ....... 41 Lenses . . . . . . . .44 Converging Lenses ...... 44 Diverging Lenses . . . . . . .44 Vision and the Eye ...... 46 Adjustment of the Eye Use of Spectacles . . . .48 The Punctum Coacum ...... CO 6 CONTENTS. PAC. E Persistence of Impressions . . . . . .61 Bodies seen within the Eye ..... 52 The Stereoscope . . . . . . .64. Nature of Light, Physical Theory of Eeflection and Ecfraction 57 Theory of Emission . . ... . . 67 Theory of Undulation . . . . . .69 Prisms .... .... 64 Prismatic Analysis of Light Dispersion . . . .65 Invisible Eays Oalorescence and Fluorescence . . . C6 Doctrine of Visual Periods . . . . . .08 Doctrine of Colors . . . . . . 69 Chromatic Aberration. Achromatism . . . .71 Subjective Colors ....... 72 Spectrum Analysis . . . . . . .71 Further Definition ofEadiation and Absorption ... 75 The pure Spectrum Fraunhofers Lines . . . .77 Eeciprocity of Kadiation and Absorption ... 78 Solar Chemistry . . . . . .80 Planetary Chemistry . . . . . .81 Stellar Chemistry . . . . . . .82 Nebular Chemistry ...... 82 The Eed Prominences and Envelope of the Sun . . .82 The Eainbo-fir ....... 84 Interference of Light . . . . . . .86 Diflraction, or the Inflection of Light . . . . 88 Measurement of the Waves of Light . . . . .93 Colors of Thin Plates . . . . . .96 Double Eefraction . . . . . . ...