Vlll. PREFACE. 



practical measurements are given in full, many other 

 experiments are only alluded to, and left to the student 

 to carry out with such modifications as his experience may 

 suggest. 



The experiments may be taken as a general outline for 

 a course of practical work in the laboratory ; but as the 

 student makes progress he should learn to depart more 

 and more from the exact form given in the book, and 

 endeavour by different ways to familiarise himself with 

 the behaviour of the machines he is handling. He must 

 not forget that a large part of the " experiment " is 

 actually to be done on paper after the readings have been 

 taken. 



The experimental results given in the various tables 

 and curves were, with few exceptions, obtained expressly 

 for the purpose of this book. The greater part of this 

 arduous work was actually carried out by the writer's 

 friend, Mr. U. A. Oschwald, B.A., without whose assistance 

 the book could hardly have appeared in its present form. 



The author wishes to record his indebtedness to Mr. 

 Oschwald for this help and for assistance in the final 

 revision. 



He has also to thank his friend, Mr. W. H. F. Murdoch, 

 B.Sc., for very kindly reading through the proofs, and 

 for making numerous valuable suggestions. Mr. S. 

 Irwin Crookes has kindly pointed out several errors, 

 and suggested improvements in certain details. 



