This Book is Dedicated to BALFOUR STEWART and

P. C. JULES JANSSEN, Encouraged by One

Friend I undertook the Work which has brought me The Other.

PREFACE.

THE present volume has grown out of an intention I formed about a year ago, to publish the Papers I had communicated to the Royal Society, dealing with the new facts which a new method of inquiry had revealed to us. I formed this resolution because, doubtless owing to their being scattered among the publications not easily procurable of a learned body, these Papers were evidently unread by some who were actually engaged, as well as by many who were merely interested, in the inquiry.

It next struck me that it would be wise to relieve the great-I fear too-great-terseness of these Papers by introducing into the same volume three Lectures I had also published in the Proceedings of the Royal Institution, giving an account of the first outcome of my inquiries, and of the results of the two Eclipse Expeditions which I had accompanied to the

Mediterranean and India. After I had determined to appeal by the publication of these to a wider public, I chanced to fall upon the notes of a course of four other Lectures on the Sun which I had also given in the Royal Institution, but which remained unpublished, and were almost forgotten. This decided me to attempt to make the story of the work more complete, and to add to it the information necessary for the general reader both as to the telescopic and spectroscopic sides of the inquiry, by means of these notes and some of the Essays which I had published at different times during the last ten years in The Reader, Macmillan's Magazine (these were written in conjunction with my friend Dr. Balfour Stewart), Nature, the Times, Daily News, and other periodicals.

This, then, is the origin of the work in its present shape.

In the First Part I have attempted to give a sketch of the various inquiries into the Physical Constitution of the Sun, and I have not hesitated to alter the arrangement of the four Lectures, and, in some cases, the Essays to which I have referred, so as to make the story a continuous one. I have not only largely added to the parts dealing with Spectrum Analysis, but I have given a body of

information on this new science in its special relation to its solar applications which I hope may be found

of value.

The Second Part, which consists of my Papers communicated to the Royal Society and to the French Academy of Sciences, of course is given verbatim, with the exception of the references to the illustrations, many of which have been transferred to the First Part of the book. To these Papers I have added Notes, on some of the more fundamental outcomes of the research, in which I have attempted to show the relations of my observations to those made by others; on the objections urged against some of the conclusions to which I had been led; and on the new facts acquired to Science by the labours of my fellowworkers. On this latter point, however, I have been compelled not only to give slight references where I could have wished to have given full details, but to cancel much matter actually written in order to keep the volume within convenient limits.

I must, however, thank Professors Young and Respighi for permitting me to largely increase the value of my book by referring at the length I have done to their observations. The faithful translation of the memoirs of the illustrious Italian observer here