vi PREFACE 



who have thus unwittingly contributed are: G. H. Parker, 

 W. C. Curtis, and M. F. Guyer. 



In the preparation of the book the writer has been under 

 obligation to a number of persons, and it is a pleasure to 

 acknowledge the debt. Professor M. F. Guyer read the 

 manuscript for chapters I to V, XXVII, XXVIII, XXX, 

 and helped in other ways; Professor George Wagner, read 

 chapters XI to XX; Professor W. S. Marshall, V to XI; 

 Professor W. J. Meek, XXVII; Dr. John N. Lowe, I to 

 IV; Miss G. M. White, XXI and XXII; Messrs. A. R. 

 Cahn and T. C. Nelson, XXV and XX respectively. Dr. 

 A. G. Ruthven and Professor E. C. Case, of the University 

 of Michigan, read chapters XXIII, XXIV, XXVI and 

 XXIX. Most of all I am indebted to Miss Hattie J. 

 Wakeman, who drew all the original figures but two. Fig. 

 46 was drawn by Lydia Wakeman, and Mr. A. R. Cahn 

 furnished the prints for Fig. 103. 



UNIVERSITY OP WISCONSIN, 

 March 1, 1917. 



