Vl PREFACE 



quoted wherever obtainable, as their employment tends 

 to counteract vagueness. 



It will be noticed that many of the researches dealt 

 with are as yet incomplete, but in a rapidly advancing 

 science one is compelled to agree with James Stephens 's 

 Philosopher's remarks concerning his stirabout: "Finality 

 is death. Perfection is finality. Nothing is perfect. 

 There are lumps in it." 



In conclusion, I wish to express my great indebtedness 

 to Professor H. H. Dixon for his continuous advice and 

 criticism throughout the preparation of the book, and 

 for his kindness in reading the proofs. My thanks are 

 also due to Professor Sydney Young for revising Chapter V., 

 which deals with osmotic pressure. In addition I am 

 under an obligation to those of my friends who gave me 

 help by sending me copies of their papers or in other ways, 

 and to Miss R. R. A. Colthurst for reading the proofs. 



TRINITY COLLEGE, DUBLIN, 

 January, 1916. 



