vi PREFACE 



year if five hours per week be devoted to the subject. It is possible, 

 however, by judicious selection of the matter to be dealt with by 

 demonstration, to cover the ground in the course of the year when 

 demands upon the time-table will permit only four hours per week to 

 be given to science teaching. 



The questions at the ends of the chapters are taken from the 

 Intermediate Examination papers ; and acknowledgment is gratefully 

 made of the courtesy of the Assistant Commissioners in permitting 

 these to be used. 



I have to express my gratitude to Prof. II. A. Gregory and Mr. A. T. 

 Simmons for permission, of which I have fully availed myself, to 

 use the subject-matter and diagrams in their numerous text-books, 

 and also for much valuable advice and criticism while the book was 

 passing through the press. 



GEORGE A. WATSON. 



September 1918. 



