INTRODUCTION xv 



In recent years much has been done both in Germany and 

 in the United States of America to increase our knowledge 

 of the physical properties of soils. Since 1878, a periodical 

 edited by E. Wollny, Forschungen auf dem Gebiete der 

 Agriculturphysik, has been devoted to the publication of 

 papers on this subject. In America the study of the soils 

 characteristic of several States and districts has been ener- 

 getically carried on by Hilgard, and with a more limited 

 scope by King. Since 1893, the subject has been taken up by 

 the U. S. Department of Agriculture, at first in connexion 

 with the Weather Bureau, and since 1895 under a separate 

 Division of Agricultural Soils, superintended by Professor 

 M. Whitney. The inquiry which was at first local has thus 

 grown to be one of national application. The facts available 

 for a discussion of the subject have thus become very numerous. 

 Some of the investigations made, and some of the conclusions 

 arrived at, will be found in the following pages. 



