PREFACE vii 



photographs of apparatus, and Mr R. H. Carter, in 

 particular, for preparing the index. 



In order to facilitate any subsequent communica- 

 tions with regard to the text, and to avoid confusion, it is 

 desirable to ascribe the various sections of this volume 

 to their particular writers. They are as follows : — 

 Sections II., III., IV., and VI. (S. J. M. A); Sections 

 I. and V. (D. R. E.-K.). 



S. J. M. A., 

 Reading. 



D. R. E.-K., 



Wye, Kent. 

 September 191 2. 



