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." WORKS ON ASTRONOMY. Elements of Astronomy. By ROBERT STOWELL BALL, LL. D., F. R. S., Andrews Professor of Astronomy in the University of Dublin, Royal Astronomer of Ireland. With Illustrations. 16mo. Cloth, $2.25. Elementary Lessons in Astronomy. By J. NORMAN LOCKYER, F. R. S. Richly illustrated, and embracing the Latest Discoveries. American edition. Adapted to the Schools and Academies of the United States. 12mo. Cloth, $1.50. Outlines of Astronomy. By Sir J. J. W. HERSCHEL. With Plates and Woodcuts. Eleventh edition. 8vo. Cloth, $4.00. The Sun. By C. A. YOUNG, Ph. D., LL. D., Professor of Astronomy in the College of New Jersey. With numerous Illustrations. 12mo. Cloth, $2.00. "Professor Young is an authority on 'The Sun,' and writes from intimate knowledge. He has studied that great luminary all his life, invented and improved instruments for observing it, gone to all quarters of the world in search of the best places and opportunities to watch it, and has contributed important discoveries that have extended our knowledge of it."--_Popular Science Monthly._ Spectrum Analysis, in its Application to Terrestrial Substances, and the Physical Constitution of the Heavenly Bodies. Familiarly explained by Dr. H. SCHELLEN, Director der Realschule I. O. Cologne. Translated from the second enlarged and revised German edition by JANE and CAROLINE LASSELL. Edited, with Notes, by WILLIAM HUGGINS, LL. D. With numerous Woodcuts, Colored Plates, and Portraits; also, Angstroem's and Kirchhoff's Maps. 8vo. Cloth, $6.00.