Light And Electricity

Front matter

Tyndall

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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, summing up briefly and clearly the leading facts and principles 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 recapitulation 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 indispensable condition of 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

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

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 of Eadiation and Absorption ... 75

The pure Spectrum: Fraunhofer's 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 . . . . . . .101

Phenomena presented by Iceland Spar .... 104

Polarization of Light ...... 106

Polarization of Light by Eeflection .... 108

Polarization, of Light by Refraction . . . . .110

Polarization of Light by Double Eefraetion . . . no

CONTENTS. 7

PAGE

Examination of Light transmitted through Iceland Spar . .111

Colors of Double-refracting Crystals in Polarized Light . . 114

Rings surrounding the Axes of Crystals in Polarized Light . .119

Elliptic and Circular Polarization .... 120

Rotatory Polarization ...... 121

CONCLUSION . . . . . . .123

ELECTRICITY.

Voltaic Electricity : the Voltaic Battery . . . 131

Electro-Magnetism: Elementary Phenomena . . .133

Electro-Magnetic Engines . . . . .135

Physical Effects of Magnetization . . . . .136

Character of Magnetic Force ..... 138

Magnetism of Helix : Strength of Electro-Magnets . . . 140

Electro-Magnetic Attractions : Law of Squares . . . 140

Inference from Law of Squares ; Theoretic Notions . . . 143

Diamagnetism : Magne-Crystallic Action . . . 144

Frictional Electricity: Attraction and Repulsion: Conduction and

Insulation ....... 145

Theories of Electricity : Electric Fluids .... 147

Electric Induction : the Condenser :' the Electrophorns . . 148

The Electric Machine : the Leyden-jar .... 149

The Electric Current . . . . . . .150

The Electric Discharge : Thunder and Lightning . . 151

* Electric Density : Action of Points ..... 152

Relation of Voltaic to Frictional Electricity . . . 153

Historic Jottings, concerning Conduction and the Leyden-jar .155

Historic Jottings, concerning the Electric Telegraph . . 166

Phenomena observed in Telegraph-Cables .... 159

Artificial Cables ....... 163

Sketch of Ohm's Theory and Kohlrausch's Verification . . 165