CONTENTS.—On the Relation of Natural Science to Science in General.—On Goethe's Scientific Researches.—On the Physiological Causes of Harmony in Music.—Ice and Glaciers.—Interaction of the Natural Forces.—The Recent Progress of the Theory of Vision.—The Conservation of Force.—Aim and Progress of Physical Science.

CONTENTS.—Gustav Magnus.—In Memoriam.—The Origin and Significance of Geometrical Axioms.—Relation of Optics to Painting.—Origin of the Planetary System.—On Thought in Medicine.—Academic Freedom in German Universities.

"Professor Helmholtz's second series of 'Popular Lectures on Scientific Subjects' forms a volume of singular interest and value. He who anticipates a dry record of facts or a sequence of immature generalization will find himself happily mistaken. In style and method these discourses are models of excellence, and, since they come from a man whose learning and authority are beyond dispute, they may be accepted as presenting the conclusions of the best thought of the times in scientific fields."—Boston Traveler.

"Of the essays that have been collected by Professor Huxley in this volume, the first four deal with some aspect of education. Most of the remainder are expositions of the results of biological research, and, at the same time, illustrations of the history of scientific ideas. Some of these are among the most interesting of Professor Huxley's contributions to the literature of science."—London Academy.

"It is refreshing to be brought into converse with one of the most vigorous and acute thinkers of our time, who has the power of putting his thoughts into language so clear and forcible."—London Spectator.

These essays are an outcome of a somewhat large experience in teaching physical science to college students. Cambridge, Massachusetts, early set the example of making the student's own observations in the laboratory or cabinet the basis of all teaching, either in experimental or natural history science; and this example has been generally followed. "But in most centers of education," writes Professor Cooke "the old traditions so far survive that the great end of scientific culture is lost in attempting to conform even laboratory instruction to the old academic methods of recitations and examination. To point out this error, and to claim for science-teaching its appropriate methods, was one object of writing these essays."