AUTHOR’S PREFACE. 
vii 
debted to many scholars, some of whom are 
mentioned in the appropriate place in order 
that readers may become familiar with their 
names. I may add here Prof. Joseph LeConte, 
James Dwight Dana, R. S. Tarr, A. P. Brig¬ 
ham, C. Flammarion, Silnon Newcomb, John 
Ferrell, Pres. D. S. Jordan, and Marshall, Ro¬ 
manes, Huxley, Darwin, and Wallace. Also to 
E. Hazel Troeger, who has given me valuable 
assistance in the preparation of the book and 
the reading of the proofs. 
The Plan and Scope of the Seeies. 
The general plan of the series has been 
steadily kept in view, namely: 
1. To provide a graded course of reading 
on elementary science, or what is called Nature 
Study topics. It seems desirable to have the 
reading as helpful as possible to the regular 
work of the school, and particularly geography 
and literature, for the former depends large¬ 
ly upon nature’s phenomena, and the latter 
abounds in references to birds and flowers, 
beasts and plants, and to the phases of the 
skies, winds, and water; both become more in¬ 
teresting and intelligent to him who has read 
such a course; and 
