Yew, 141. _Yucca_, 153. _Zanthoxylum_. See "Prickly ash." _Zingiber_, _-aceæ_. See "Ginger." Zoölogy, 2. Zoöspore, 25, 37, 58, 62. _Zygnema_, 33; Fig. 19. Zygomorphy, Zygomorphic, 164, 215, 226. NATURAL SCIENCE. _Elements of Physics._ A Text-book for High Schools and Academies. By ALFRED P. GAGE, A.M., Instructor in Physics in the English High School, Boston. 12mo. 424 pages. Mailing Price, $1.25; Introduction, $1.12; Allowance for old book, 35 cents. This treatise is based upon _the doctrine of the conservation of energy_, which is made prominent throughout the work. But the leading feature of the book--one that distinguishes it from all others--is, that it is strictly _experiment-teaching_ in its method; _i.e._, it leads the pupil to "read nature in the language of experiment." So far as practicable, the following plan is adopted: The pupil is expected to accept as _fact_ only that which he has seen or learned by personal investigation. He himself performs the larger portion of the experiments with _simple_ and _inexpensive_ apparatus, such as, in a majority of cases, is in his power to construct with the aid of directions given in the book. The experiments given are rather of the nature of _questions_ than of illustrations, and _precede_ the statements of principles and laws. Definitions and laws are not given until the pupil has acquired a knowledge of his subject sufficient to enable him to construct them for himself. The aim of the book is to lead the pupil _to observe and to think_. C. F. EMERSON, _Prof. of Physics, Dartmouth College_: It takes up the subject on the right plan, and presents it in a clear, yet scientific, way. WM. NOETLING, _Prof. of Rhetoric, Theory and Practice of Teaching, State Normal School, Bloomsburg, Pa._: Every page of the book shows that the author is a _real_ teacher and that he knows how to make pupils think. I know of no other work on the subject of which this treats that I can so unreservedly recommend to all wide-awake teachers as this. B. F. WRIGHT, _Supt. of Public Schools, St. Paul, Minn._: I like it better than any text-book on physics I have seen. O. H. ROBERTS, _Prin. of High School, San Jose, Cal._: Gage's Physics is giving great satisfaction. _Introduction to Physical Science._ By A. P. GAGE, Instructor in Physics in the English High School, Boston, Mass., and Author of _Elements of Physics_, etc. 12mo. Cloth. viii + 353 pages. With a chart of colors and spectra. Mailing Price, $1.10; for introduction, $1.00; allowance for an old book in exchange, 30 cents. The great and constantly increasing popularity of Gage's _Elements of Physics_ has created a demand for an equally good but easier book, on the same plan, suitable for schools that can give but a limited time to the study. The _Introduction to Physical Science_ has been prepared to supply this demand.