PREFACE. 



The diagrams are of simple character, intended to show 

 as clearly as possible the particular points desired. Those 

 on pages 324 to 327 are from blocks kindly lent by the 

 Highland and Agricultural Society of Scotland, to whom 

 the author desires to express his thanks. 



The author wishes here to express his indebtedness to 

 many friends for assistance in various ways ; particularly 

 would he thank his friend and colleague Dr. J. McCrae 

 for valuable help in correcting the proofs. He would 

 also acknowledge the assistance of one of his students Mr. 

 Herbert Hunter who has kindly prepared the index. 



LEEDS, March, 1902. 



