Transcriber’s Note When italics were used in the original book, the corresponding text has been surrounded by _underscores_ Mixed fractions have been displayed with a hyphen between whole number and fraction for clarity. Superscripted characters are preceded by ^ and when more than one character is superscripted, they are surrounded by {}. Subscripted characters are preceded by an underscore and surrounded by {}. Some corrections have been made to the printed text. These are listed in a second transcriber’s note at the end of the text. ON MOLECULAR AND MICROSCOPIC SCIENCE VOLUME THE FIRST _By the same Author._ ON the CONNECTION of the PHYSICAL SCIENCES. 9th Edition. Portrait. Post 8vo. 9_s._ PHYSICAL GEOGRAPHY. New Edition, thoroughly revised. Portrait. Post 8vo. [_In the press._ [Illustration: _Fig. 89, p. 20._ EUCYRTIDIUM CRANOIDES. [_Frontispiece to Vol. I._ ] ON MOLECULAR AND MICROSCOPIC SCIENCE BY MARY SOMERVILLE AUTHOR OF ‘THE MECHANISM OF THE HEAVENS’ ‘PHYSICAL GEOGRAPHY’ ‘CONNECTION OF THE PHYSICAL SCIENCES’ ETC. _Deus magnus in magnis, maximus in minimis_—St. Augustine IN TWO VOLUMES—VOL. I. WITH ILLUSTRATIONS LONDON JOHN MURRAY, ALBEMARLE STREET 1869 _The right of translation is reserved_ LONDON: PRINTED BY SPOTTISWOODE AND CO., NEW-STREET SQUARE AND PARLIAMENT STREET PREFACE. MICROSCOPIC INVESTIGATION of organic and inorganic matter is so peculiarly characteristic of the actual state of science, that the Author has ventured to give a sketch of some of the most prominent discoveries in the life and structure of the lower vegetable and marine animals in addition to a few of those regarding inert matter. The Author feels bound to return her best thanks to kind friends—Sir John Herschel, Mr. Huggins, Mr. Gwyn Jeffrey, Prof. Tyndall, and Mr. T. Moore of Chelsea, who have aided in revising some of the sheets for press, and have thus counteracted the disadvantage under which she labours, of a residence abroad, and at a distance from libraries of reference. CONTENTS OF THE FIRST VOLUME. PART I. ATOMS AND MOLECULES OF MATTER. SECT. PAGE I. ELEMENTARY CONSTITUTION OF MATTER 1