PREFACE 
to see more clearly how the human race grows ever more 
primitive, increasingly less like that of today and definitely 
inferior to it in many ways, the farther back we go in point 
of time. 
The account of man’s conquest of material things, how- 
ever, from his primeval condition to the beginnings of 
modern civilization, contained in the last nine chapters, 
has called for the opposite method of treatment. Instead 
of tracing them backward through the ages, the various 
discoveries and inventions of major importance have been 
dealt with in their probable order of occurrence, and their 
application to an ever-growing range of uses has been 
described. 
Where so many have been drawn on for information, it 
would be impossible to give due credit by name in each 
individual instance. Special acknowledgment must be 
made, however, to Dr. H. N. Russell, Sir James Jeans, and 
Dr. A. S. Eddington, among astronomers; to Dr. T. C. 
Chamberlin, Dr. R. D. Salisbury, Dr. Ernst Antevs, Dr. 
C. Wi Gilmore): Dr: Ry-S.) Bassler, the (ace Wore PD: 
Walcott, and the late Dr. G. P. Merrill, among geologists 
and paleontologists; to Dr. E. W. MacBride, Dr. C. W. 
Prentiss, Dr. L. B. Arey, and Dr. Edwin G. Conklin, 
among cytologists and embryologists; and to Sir Arthur 
Keith, M. Marcellin Boule, the Abbé H. Breuil, Dr. G. G. 
MacCurdy, Dr. Hugo Obermaier, and Dr. H. F. Osborn, 
among prehistorians. 
For the various illustrations, due acknowledgment is 
made in the captions accompanying each. Hearty thanks 
must be paid to Mr. William H. Gill, of Washington, for 
the artistic excellence of the drawings, which are almost 
entirely the result of his painstaking work. 
The writer also wishes to express his personal apprecia- 
tion to Miss Daisy Furscott, of the Freer Gallery Expedi- 
tion Library, for her aid in reference work and her helpful 
criticism; and to Miss Christabel E Hill for her unremit- 
ting care in the preparation of the manuscript. 
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