VOL. XLIX.] ESTABLISHED BY EDWARD L. YOUMANS. [No. 6. APPLETONS' POPULAR SCIENCE _ MONTHLY. ft OCTOBER, 1896. EDITED BY WILLIAM JAY YOUMANS. CONTENTS. P AGB I. The Metric System. By Prof. T. C. MENDENHALL ............... 721 *W II. Nevada Silver. By CHABLES HOWABD SHINN (Illustrated.) ...... 734 III. A Measure of Mental Capacity. By Dr. EMIL KRAEPELIN ..... . . 756 IV. Some Beginnings in Science. By Prof. COLLIER COBB. (Illus.) . . . 763 V. The Vivisection Question. By Prof. C. F. HODGE. (Concluded.) . . 771 VI. Acetylene, the New Illuminant. By V. J. YOUMANS ............. 786 VH. The Significance of Leaves. By F. SCHUTLER MATHEWS. (Illus.) . 793 VIII. The Educative Value of Children's Questioning. By H. L. CLAPP. . 799 IX. The Self and its Derangements. By Prof. W. ROMAINE NEWBOLD. 810 X. Exaggeration as an ^Esthetic Factor. By M. F. REGNATJLT ....... 821 XL Enrico Ferri on Homicide. By HELEN ZIMMERN. (Second Paper.). 828 XII. Sketch of Robert Empie Rogers. (With Portrait.) .............. 837 XIII. Correspondence : Woman's Claims to the Ballot A Correction .......... 842 XIV. Editor's Table : Another Bishop on Science Teaching in Elementary Schools. The Fourth Buffalo Meeting of the American Association ........... 843 XV. Scientific Literature ........................................... 846 XVI. Fragments of Science ......................................... 855 XVII. Index to Volume XLIX ....................................... 865 NEW YORK: D. APPLETON AND COMPANY, 72 FIFTH AVENUE. SINGLE NUMBER, 50 CENTS. YEARLY SUBSCRIPTION, $5.00. COPYRIGHT, 1896, BY D. APPLETON AND COMPANY. Entered at the Post Office at New York, and admitted for transmission through the mails at second-class rates. Just as Good a. i Scott's Emulsior You hear it in nin< \ out of ten drug stores It is the reluctan testimony of 40,00( druggists that Scott' Emulsion is the stan dard of the world: ; t i And isn't the kind all others try to range up to, the kind B you to buy? Two sizes, 50 cts. and $1.00. THE METRIC SYSTEM. 733 commercial arithmetic none is comparable to that of expressii shmings, pence, and farthings as decimals of a pound. The are fl^reby put almost upon as good a footing as if the country possessed the advantage of a real decimal coinage." He then proceed^ to develop rules by means of which any sum o money nmy be expressed in pounds and decimals exacly as our money is always expressed in dollars and decimals, s^that any re- quired operation may be easily performed by the common rules of arithmetic, y^fter this the decimals of a poun(L