RADIATION

BY P. PHILLIPS

D.Sc. (B'HAM), B.Sc. (LONDON), B.A. (CANTAB.)

LONDON: T. C. & E. C. JACK
67 LONG ACRE, W.C., AND EDINBURGH
NEW YORK: DODGE PUBLISHING CO.
1912

CONTENTS

CHAP.

INTRODUCTION

I. THE NATURE OF RADIANT HEAT AND LIGHT

II. GRAPHIC REPRESENTATION OF WAVES

III. THE MEANING OF THE SPECTRUM

IV. THE LAWS OF RADIATION

V. FULL RADIATION

VI. THE TRANSFORMATION OF ABSORBED RADIATION

VII. PRESSURE OF RADIATION

VIII. THE RELATION BETWEEN RADIANT HEAT AND ELECTRIC WAVES

INDEX

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INTRODUCTION

We are so familiar with the restlessness of the sea,and with the havoc which it works on our shippingand our coasts, that we need no demonstration toconvince us that waves can carry energy from oneplace to another. Few of us, however, realise thatthe energy in the sea is as nothing compared withthat in the space around us, yet such is the conclusionto which we are led by an enormous amount ofexperimental evidence. The sea waves are only nearthe surface and the effect of the wildest stormpenetrates but a few yards below the surface, while thewaves which carry light and heat to us from the sunfill the whole space about us and bring to the eartha continuous stream of energy year in year out equalto more than 300 million million horsepower.

The most important part of the study of Radiationof energy is the investigation of the characters of thewaves which constitute heat and light, but there isanother method of transference of energy includedin the term Radiation; the source of the energybehaves like a battery of guns pointing in alldirections and pouring out a continuous hail of bullets,which strike against obstacles and so give up theenergy due to their motion. This method is relativelyunimportant, and is usually treated of separatelywhen considering the subject of Radioactivity. Weshall therefore not consider it in this book.

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RADIATION

CHAPTER I

THE NATURE OF RADIANT HEAT AND LIGHT

Similarity of Heat and Light.—That light andheat have essentially the same characters is verysoon made evident. Both light and heat travel tous from the sun across the ninety odd millions ofmiles of space unoccupied by any material.

Figure 1

Both are reflected in the same way from reflectingsurfaces. Thus if two parabolic mirrors be placedfacing each other as in the diagram (Fig. 1), with asource of light L at the focusof one of them, an invertedimage of the light will beformed at the focus I of theother one, and may bereceived on a small screen placed there. The pathsof two of the rays are shown by the dotted lines.If L be now replaced by a heated ball and a[...