a certain ratio; and, if 16 be called 1, 48 will be 3, 80 will be 5, 112 will be 7, and 144 will be 9, etc. These distances may then be expressed as falling distances, thus, 1, 3, 5, 7, 9, etc. And, keeping in mind that the horizontal velocity remains uniform, that is 48 ft., i. e., 3 x 16 ft. in a second, we have two kinds of dimensions at right angles to each other, from which to make the curve. This curve is called a parabola. 442. Can you construct a parabola? When these distances, instead of being written down as the separate result of each second's action, are successively added to show the combined results, we have for— From this it will be seen that the distance fallen is as the square of the time, i. e., in 6 seconds the distance fallen will be 62 x 16 ft. = 36 X 16 ft. = 576 ft. 443. Required the distance a stone falls in half a second. 4, 444. Required the distance a stone falls in 21 seconds. 3 445. Can you show that there are two kinds of quadrilaterals in which the diagonals must be equal, two kinds where they may be equal, and two kinds where they cannot be equal? 446. Can you make in card a tetrahedron whose four surfaces shall be unlike in form? 9 THE END. IN SCIENCE, HISTORY, AND LITERATURE. 18mo. Flexible cloth, 45 cents each. SCIENCE PRIMERS. Edited by Professors HUXLEY, ROSCOE, and BALFOUR STEWART. Introductory. Prof. T. H. Hux- | Astronomy. J. N. LOCKYER, LEY, F. R. S. Physical Geography. Prof. A. GEIKIE, F. R. S. F. R. S. F. R. S. Botany. Sir J. D. HOOKER, F.R.S. Pianoforte. FRANKLIN TAYLOR. Natural Resources of the HISTORY PRIMERS. Edited by J. R. GREEN, M. A., Examiner in the School of Modern The object of these primers is to convey information in such a manner as to make it both intelligible and interesting to very young pupils, and so to discipline their minds as to incline them to more systematic after-studies. The woodcuts which illustrate them embellish and explain the text at the same time. New York: D. APPLETON & CO., 1, 3, & 5 Bond Street. ENGLISH and AMERICAN LITERATURE, Forming the Second Volume of "Literature Primers," EDITED BY J. R. GREEN, M. A., Examiner in the School of Modern History at Oxford, AND CONTAINING ENGLISH LITERATURE. BY STOPFORD BROOKE, M. A. AMERICAN LITERATURE. By J. H. PATTON, M. A. In one volume. Flexible cloth, 45 cents. From the New York Observer. "D. Appleton & Co. have published (in their series of 'Lit erature Primers') a new edition of Stopford Brooke's 'English Literature,' with a valuable addition on American Literature. Into about twenty pages Mr. Patton has condensed a summary of the principal American writers on the several departments of letters, with a brief indication of the character of their works, bu without attempting a catalogue. Few of the leading writers of the two centuries are omitted. The book will be very useful as a text-book, and also for reference. For schools its value is much increased by the series of suggestive questions appended." D. APPLETON & CO., PUBLISHERS, 1, 3, & 5 BOND STREET, N. Y. |