Miss Edna Doughty

8-29-1925

ΤΟ

DR. WM. HUGGINS, F.R.S., LL.D., F.R.A.S.

-THE HERSCHEL OF THE SPECTROSCOPE

IN RECOGNITION OF THOSE LABOURS BY WHICH THE WHOLE

ASPECT OF MODERN ASTRONOMY HAS BEEN MODIFIED

This Work is Dedicated

BY

THE AUTHOR.

PREFACE.

WHEN I had completed my treatise on Saturn and its System, I formed the design of preparing a separate treatise on each of the planets Mars and Jupiter, and then another and larger treatise on the Sun. Circumstances, which it is needless to particularize, prevented me from carrying out this design at that time, and indeed threatened to withdraw my attention altogether from scientific pursuits. That my plans, though delayed, have not been lost sight of during the last four years, is evidenced by the appearance of many papers of mine on Mars, Jupiter, and the Sun, in several quarterly, monthly, and weekly journals. These, if collected, would of themselves suffice to form volumes of no inconsiderable dimensions on these several orbs; while my Other Worlds than Ours' presents a sort of summary of my researches on these and other astronomical subjects. But it is only quite recently that I have been able to resume my original design.

The delay has not been without its advantages, however. A work on the Sun has at the present time a far greater interest than it would have had four years since; while I have been able to obtain a much wider and more complete view of the subject than I should

probably have thought necessary had I completed the work at that time.

My primary object in the present volume has been to furnish a full account of the remarkable discoveries which have been effected by observers of the Sun, whether by means of the telescope, the spectroscope, polariscopic analysis, or photography. It will be seen. that Chapters IV., V., and VI., in which I deal with these discoveries, together constitute more than one half of the main text. In these chapters the labours of the Herschels, Schwabe, Carrington, Secchi, De la Rue, Stewart, and others in examining the solar surface; the later observations of Huggins, Zöllner, Respighi, Secchi, Lockyer, Young, and others in the study of the prominences and chromosphere; and the observations which have been made during the past two centuries on the phenomena presented by the solar corona, have been dealt with at considerable length.

But it seemed desirable that a separate and complete explanation should be given of all those matters which specially appertain to the application of spectroscopic analysis to the study of solar physics. Without an account of these matters, many of the most interesting discoveries made in recent times would be almost unintelligible, and it did not seem fitting to refer the general reader to the valuable but costly works of Roscoe and Schellen. Further, I think such a mode of treating spectroscopic analysis as I have adopted in

Chapter III. of this work, more likely to be of use to the reader than a fuller but less simple account. In one respect, indeed, Chapter III. presents what is wanting in every treatise on the analysis which I have hitherto seen the matter in pp. 128-156 exhibits what really happens when the light from the object studied is sent through a battery of prisms. In Chapter III. I give an account of the principles of Browning's automatic spectroscope, and exhibit a plan of my own by which this principle may be extended so as to include a second battery. I think that in future applications of spectroscopic analysis, the plan illustrated at p. 139 is likely to be found of considerable utility.

Another large section of the book is devoted to the question of the Sun's distance. In Chapter I. will be found a very full account (the fullest popular account yet published, I believe) of the researches which have been made up to the present time into this subject: while in Appendix A the transits of 1874 and 1882 (already attracting much notice) are dealt with at length, and the best means for observing them effectively are fully considered. The subject is one to which I have given much attention. In constructing the pictures from which Plates IX. and X. have been reduced (by photolithography), every circumstance of the transit of 1874 was taken most carefully into account; and I think that I may safely say of these views, the four which accompanied them in Vol. XXIX. of the Astro