PREFACE vii 



the essays, whose willingness to accede to the 

 editor's request for contributions calls for a word 

 of cordial acknowledgment, to present the results 

 of experience in scientific investigation, to illustrate 

 by concrete examples the sources of progress in a 

 few departments of knowledge and so make clear 

 to the layman the position of research as a factor 

 in national prosperity. 



It is an especial pleasure to thank Lord Moulton 

 for contributing an Introduction. 



A. C. SEWARD 



DOWNING COLLEGE LODGE 

 January 5, 1917 



