Preface vii 



industry of transportation, special points of view, purposes, 

 and methods emerge, which are defined gradually and appro- 

 priately to the students' needs and interests and in such a way 

 as to lead them to organize what they know and think about 

 the subjects. It is recognized, to quote the words of Professor 

 Dewey, that "it is only because we have different interests or 

 different ends, that we sort out the material and label part of 

 it science, part, history, part, geography, and so on." So with 

 the differentiation of science into its conventional branches 

 it must be an objective, and not the beginning of scientific 

 study; and progress in making such divisions depends upon 

 needs, interests, and ends. 



(4) Emphasis is constantly placed upon the utility of a scien- 

 tific understanding of things in acquiring a better control and 

 use of them for the purposes and welfare of mankind. 



(5) The study of projects suitable to a given class or place is 

 facilitated by the abundance of material which the book affords. 

 The book provides sufficient work for a year, with opportunities 

 for selection to meet special requirements. For a half-year 

 course selections may be made readily by the aid of the topics 

 into which the chapters are divided. 



In the preparation of the book, which has extended over a 

 period of six and more years, a great indebtedness to many 

 teachers and scientific works has been incurred. The use of 

 the information and help thus gained is such as to make specific 

 mention of sources almost impossible ; general acknowledg- 

 ment is made with gratitude and appreciation. It is a pleasure 

 to express our obligation to Professor George I. Finlay of New 

 York University for helpful criticisms made in the manuscript ; 

 to Ivy G. Smith for untiring help in preparing the manuscript, 

 for many of the drawings, and for the index ; and to The Mac- 

 millan Company for generous cooperation in practically every 

 stage of the making of the book. 



NEW YORK CITY, 



May 20, 1918. 



