PREFACE TO THE THIRD EDITION, 



IT is now seven years since the first edition of this work was pub- 

 lished, and during this short period very great advance has been made 

 in many branches of microscopical enquiry, both in this country and 

 on the Continent. 



Since the publication of the original work, Messrs. Powell and 

 Lealand have succeeded in making, at the request of the author, an 

 object-glass magnifying 1,800 diameters. He hopes shortly to receive 

 from them a power as much superior to this as the -^th is to the 

 old T Vth. Microscopical science is greatly indebted to these makers 

 for the advances made by them upon several occasions in the manu- 

 facture of object-glasses, and in the construction of microscopes. 



The author has considered it better to divide the work into 

 chapters instead of lectures, but the original style has been retained, 

 because it was thought to be well adapted for the description of 

 practical details, in which clearness is of far greater importance than 

 elegance of expression. 



The book now contains more than twice the amount of work in 

 the last edition. Many of the paragraphs have been re-written, and 

 three new chapters, containing nearly one hundred pages have been 

 introduced. The number of plates has been increased from 32 to 56. 



The author has still further improved upon the mode of injection 

 and preparation of tissues advocated by him and now adopted by 

 many observers. In this edition the details of the particular method 

 of preparation carried out by the author in his investigations with 

 the aid of the highest magnifying powers yet made, are for the first 

 time published. 



For the beautiful photograph which forms the frontispiece the 

 author is indebted to his friend Dr. Maddox, who has also afforded 

 him very great assistance in writing the chapter on photography. 

 This is one of the most valuable chapters in the book. It contains 

 the results of many years' most earnest work, by one of the most 

 successful workers in this department of photography. The detail 

 of some of the photographic illustrations is so very minute, that many 

 points cannot be seen by the unaided eye. A lens of low magnifying 



