University of Virginia Library

PREFACE.

THE conditions under which this work was first published are stated in the preface to the first edition, reprinted below. Although the book has been long out of print, the author has not been able to revise it for a new edition until now, and returning to this work of his youth, after twenty years of active life, he has found nothing in the tone or sentiments of the book which he desired to change. Indeed, larger knowledge has only served to confirm the general convictions therein expressed. But, of necessity, the discovery of new facts and changes in scientific theories have required alterations of phraseology in many places, and more experience has led to greater caution in the statement of conclusions. It was the author's first intention to re-write the whole book on a different plan, and in retaining the popular style of the first edition he has yielded to the judgment of friends who thought that the book would be more useful in its early, fresh form. The discussion of the

principles of crystallography in the first edition has been omitted in the revision, because found too abstruse for popular reading; but the place has been more than supplied by the new matter which has been added. The work is solely a popular exposition of the subjects on which it treats, and this design has precluded a fuller discussion of many points, as well as that precision of statement which might be expected in a more formal essay. By vote, recorded in their proceedings of March 6, 1875, the Directors of the Brooklyn Institute released to the author their copyright in the original work, and he would here express his grateful appreciation of this courtesy.

NEWPORT, September 30, 1880.