vi PREFACE. 



tion a large number of the disputed points, which I have 

 been able to investigate during the preparation of the work, 

 must have been left untouched. 



My special thanks are due to Mr Sedgwick, who has 

 not only devoted a very large amount of time and labour to 

 correcting the proofs, but has made for me an index of this 

 volume, and has assisted me in many other ways. 



Dr Allen Thomson and Professor Kleinenberg of Mes- 

 sina have undertaken the ungrateful task of looking through 

 my proof-sheets, and have made suggestions which have 

 proved most valuable. To Professors Parker, Turner, and 

 Bridge, I am also greatly indebted for their suggestions 

 with reference to special chapters of the work. 



