PREFACE TO THE FIFTH EDITION. 



THIS edition has been enlarged nearly one-half by the elaboration of the mat- 

 ter in the previous edition, and by the addition of a wholly new chapter on 

 photo-micrography and on photographing natural history objects in a hori- 

 zontal position with a vertical camera. The figures have been distributed in the 

 text, and many new ones added. 



It is hoped that the book as it now appears may, while remaining strictly ele- 

 mentary, still more fully meet the needs of those who wish to use the microscope 

 for serious study and investigation. The aim has been to produce a book for be- 

 ginners in microscopy, such as the author himself felt sorely the need of when he 

 began the study. This purpose has been strengthened and furthered by noting the 

 difficulties of the various classes that have used the work and aided in its evolution 

 during the last fifteen years. 



The author wishes to acknowledge the aid rendered by the various Optical Com- 

 panies for information freely given, and for the loan of cuts and instruments 

 (Bausch & Lomb Optical Co., Gundlach Optical Co., Queen & Co., and all the op- 

 ticians mentioned in the table of tube-length, p. 10). I feel under special obliga- 

 tion to my various classes for the enthusiasm and earnestness with which they have 

 followed the instructions in the book, to my colleagues, Professor Wilder and In- 

 structors Hopkins and Fish for suggestion , to Mrs. Gage for criticising the manu- 

 script, reading proof, preparing the index and the original figures, to Dr. A. C. 

 Mercer for aid in preparing the chapter on photo-micrography, to Dr. M. D. Ewell 

 for information and for the loan of apparatus, and finally, to many other friends 

 who have used the previous editions, and have made suggestions whereby it is 

 hoped the present edition is greatly improved. 



I would like to repeat a part of the preface to the third and to the fourth editions, 

 and to call especial attention to the address of the Hon. J. D. Cox at the recent 

 meeting of the American Microscopical Society: "A plea for systematic instruc- 

 tion in the technique of the microscope at the university," in the Proceedings for 



Extract from the preface of the fourth edition : 



"The author would feel grateful to any person who uses this book If he would 

 point out any errors of statement that may be discovered, and also suggest modifi- 

 cations which would tend to increase the intelligibility, especially to beginners." 



From the third edition : 



" It is thoroughly believed by the writer that simply reading a work on the mi- 

 croscope, and looking a few times into an instrument completely adjusted by an- 

 other, is of very little value in giving real knowledge. In order that the knowl- 

 edge shall be made alive, it must be made a part of the student's experience by 

 actual experiments carried out by the student himself. Consequently, exercises 

 illustrating the principles of the microscope and the methods of its employment 

 have been made an integral part of the work. 



"In considering the real greatness of the microscope, and the truly splendid 



