LIGHT SCIENCE. LONDON: PRINTED BY SPOTTISWOODE AND CO., NEW-STREET SQUARE AND PARLIAMENT STREET LIGHT SCIENCE FOR LEISURE HOURS. A SERIES OF FAMILIAR ESSAYS ON SCIENTIFIC SUBJECTS, NATURAL PHENOMENA, &c. BY RICHARD A. PROCTOR, AUTHOR OF ‘THE SUN’ ‘OTHER WORLDS THAN OURS’ ‘SATURN’ ETC. ‘I bear you witness as ye bear to me, Time, day, night, sun, stars, life, death, air, sea, earth.’ _Swinburne._ _NEW EDITION._ LONDON: LONGMANS, GREEN, AND CO. 1886. PREFACE TO THE FIFTH EDITION. In preparing this edition, only those passages which have been shown by recent researches to be erroneous have been removed. It has not been thought necessary, or even desirable, to modify the wording of Essays (by changes of tense or otherwise) in such a way that, as thus modified, the Essays might have appeared in 1884. In many cases this would have been altogether misleading, whereas, with the dates prefixed to the several Essays, no misconceptions can arise. RICHARD A. PROCTOR. _PREFACE TO SECOND EDITION._ This edition has been carefully revised, and, in parts, considerably modified. Thus the Essay on Britain’s Coal Cellars has been added, and two Essays on Government Aid to Science have been removed. I may mention that my views on the subject of the last-named Essays have changed altogether since those Essays were written—certain circumstances which have come under my observation having convinced me that more mischief than advantage would result from any wide scheme for securing Government aid for scientific researches. RICHARD A. PROCTOR. LONDON: _January 1873_. _PREFACE TO FIRST EDITION._