THE sixth volume of “The Book of Nature Study” is devoted to what is styled “the Physical Environment.” This, again, is subdivided into “Meteorology, &-c.,” written by Dr. Marion I. Newbigin, and “Geology, &c.,” by Prof. W. W. Watts. The titles of these subdivisions have been omitted, curiously enough, from the headings on pp. 1 and 92. Both authors, in pursuance of the plan of the work, guide the reader towards personal observation; and Dr. Newbigin especially addresses herself to the teacher, and considers throughout how certain facts are to be brought home simply to a class. Prof. Watts's pages are therefore more closely written and more enjoyable as literature, while those of his colleague are intentionally more didactic.