PREFACE TO THE SIXTH EDITION. 



THE rapid advance in microscopical knowledge, and the great strides in the 

 sciences employing the microscope as an indispensable tool, have reacted 

 upon the microscope itself, and never before were microscopes so excellent, con- 

 venient and cheap. Indeed, the financial reason for not possessing a microscope 

 can no longer be urged by any high school or academy, or by any person whose 

 profession demands it. 



Naturally, to get the greatest good from instruments, tools, or machines of any 

 kind, the one who uses them must understand the principles upon which their 

 action depends, their possibilities and limitations. 



That the student may acquire a just comprehension of some of the fundamental 

 principles of the microscope, and gain a working acquaintance with it, this book 

 has been prepared. It is a growth of the laboratory, and has been modified from 

 time to time to keep pace with optical improvements and advancing knowledge. 



This edition has been largely rewritten. Many new figures and about ninety 

 pages of new matter have been added, and it is hoped that the student will find it 

 a real help in his efforts to become master of the modern microscope. 



SIMON HENRY GAGE, 



CORNEL University. 

 October j/, iSg6. 



