PREFACE TO SECOND EDITION. 



The demand for this book having considerably 

 exceeded the expectations of its author and the 

 comments on its utility having been so favorable 

 leads to the view that it fills a gap in microscopical 

 literature. 



In preparing for a new edition an opportunity 

 has been given for enlarging on some of the sub- 

 jects and rewriting others, so as to make them 

 conform to the changes which the last five years 

 have brought about in the construction of 

 apparatus. 



While it may be true that many of the subjects 

 might be treated much more extensively, the writer 

 has purposely refrained from doing so, because he 

 has considered it beyond the province of his inten- 

 tion and because books giving more extensive 

 information are available. 



An intending purchaser of a microscope finds it 

 more or less difficult to make a suitable selection 

 and while it is always best to consult an experi- 

 enced microscopist, the writer has endeavored to 

 convey information which, he hopes, will aid in 

 this direction. 



THE AUTHOR. 

 May, 1891. 



