Light

1884 - L I G H T - PREFACE - THIS work is, like the little treatise on Heat which I - have just published, based upon the system which, after many yearsy experience, I have adopted in my ordinary Lectures. One of my chief reasons for bringing out such volumes has been the impossibility of treating with adequate detail, in a single Session, each branch of Experimental Physics. I have always given, with the requisite experimental illustrations, the fundamental phenomena and laws of each branch - further detail being necessarily confined to two or three of them, which are varied from Session to Session. An Elementary Treatise like this will therefore supply, for the Students private reading, what time does not permit his obtaining in the Lecture-room, in those Sessions in which Light is made to hold a less prominent place than Heat, Sound, or Electricity. The book is thus not designed for those who intend to make a special study either of theoretical or of experimental Optics, but for ordinary students who wish to a . c quire - familiarity with the elements of the subject. It is in no sense a mere reprint of the article Light in the new edition of the Encyclopcedia Britannica. The plan of that work required that the subject should be treated by instalments, under very different heads and my article was necessarily limited to a simple sketch, whose main object was to co-ordinate these detached portions, some of which are not yet even written. Thus, for instance, a mere mention was made of austics, Halos, Fresnels Wave-Surface, etc. while such subjects as Focal Lines, Glories, the effect of Prisms of large angle, and the physical basis of Spectrum Analysis, were entirely omitted. This work was, unfortunately, all in type before Prof. Stokes Bumett Lectures appeared, so that I have not been able to avail myself of any part of the remarkable cumulative argument in favour of the Undulatory Theory which is the main object of. these Lectures. As the book has been prepared under the pressure of a very busy session, and as I have had but slight assistance in correcting the press, I cannot hope that it will be found altogether free froni error - CONTENTS - CHAPTER I. INTRODUCTO AN R D Y H ISTORICAL CHAPTER 11. PRELIMINASRTYA TEMENT . S CHAPTER 111. SOURCE O S F LIGHT . . . CHAPTER IV. THEORIE O S F PROPAGATI O O F NL IGHT CHAPTER V. RECTILINEAPRO PAGATI O O F NL IGHT CHAPTER VI. PAGE 1 CHAPTER VII. CHAPTER VIII. REFLECTIO OF N L IGHT . CONTENTS. CHAPTER IX. REFRACTIO OF N L IGHT . . . CHAPTER X. REFRACTIOcoNn tinuecl-C u cs . PAGE . 78 CHAPTER XI. REFRACTIO IN N A NON-HO IOGENEMOEDUISU M . 134 CHAPTER XII. ABSORPTIO m N F LUORESCENCE . . CHAPTER XIII. PRELIMINAREYM ARK O S N THE UNDULATOTRHYE ORY 1 67 CHAPTER XIV. INTERFERENCE . CHAPTER XV. DOUBLRE EFRACTIO a N P OLARISATION CHAPTER XVI. RADIATIO A N N D SPECTRUAMN ALYSIS APPENDIX . INDEX . CHAPTER I. lNTRODUCTORY AND HISTORICAL. 1. SOUND m ay be defined as any effect on the sense of I hearing, and in the same way Light may be defined as any effect on the sense of sight. This . is the purely subjective use of the terms. But both - terms are quite as - frequently used in the objective as in the subjective sense. Thus, as Sound may be defined in terms of the motion of the air in the cavity of the external ear, mechanically affecting the tympanum, so Light may be defined bythe mechanical effect produced upon the extension of the optic nerve which forms the sensitive surface of the retina...