ESSAYS, ADDRESSES, AND REVIEWS. BY JOHN TYNDALL, F.R.S. Printed By Spottiswoode AND CO. 1879. All rights reserved. PREFACE TO THE SIXTH EDITION. VOL. I. INORGANIC NATURE. I. THE CONSTITUTION OF THE ENGINE. [Illustration: FIG. 185.] The most powerful searchlight in existence at thirty. Of these two people are saying: 'Hush! There she comes, poor thing, don't.