vi PREFACE 



out because the Micro- Chemistry of Dr. E. M. Chamot, which has recently appeared, 

 treats these and indeed all matters pertaining to the chemico-physical side of 

 microscopy in an adequate manner. 



As a closing word it may be said that even an elementary book like this depends 

 for its production upon many helps. The work of others must be looked for in a 

 great library; special knowledge in allied departments must be utilized through 

 the help of colleagues; apparatus and ideas can only be put in graphic form by the 

 deft hand of the artist; and perhaps most important of all is the advice and criti- 

 cism of the friend. All of these helps the author has had in abundance, and he 

 feels grateful to each helper. 



PREFACE TO THE THIRTEENTH EDITION 



BESIDES some verbal and numerical corrections in this edition, added emphasis 

 has been placed upon Dark-field Microscopy; and some new apparatus, com- 

 bined with daylight glass, has been introduced to make its use easier and more 

 comfortable for the eyes. It is believed that this powerful agent of investigation 

 deserves very wide application. The advantages of a dark field for increasing 

 visibility has been appreciated in astronomy, time out of mind, and ever since the 

 invention of the microscope (1590); and especially for the modern compound mi- 

 croscope since the introduction of Wenham's paraboloid reflector (1850), and trun- 

 cated paraboloid (1856). 



The Corning Daylight Glass for microscope lamps has proved such a boon, that 

 an improved lamp-house, especially designed for the student laboratory, has been 

 worked out and in actual use during the last college year. It serves not only for 

 lighting the microscope, but for note- taking, drawing and reading (figs. 37, 125) 

 The author is much indebted to Dr. B. F. Kingsbury for aid in perfecting this lamp. 



Attention is again called to the method of producing line drawings from photo- 

 graphs ( 289, 3i6a). 



It is hoped that the discussion of the units of measure for microscopic objects 

 and for light waves ( 246, 406) may help to correct the confusion in this field. 

 Acknowledgement is gratefully made for help in this matter by the U. S. Bureau 

 of Standards, the Cornell University Department of Physics, and the Optical De- 

 partment of the Corning Glass Works. 



Finally, for progress in the microscopical field attention is especially called to the 

 Symposium on the Microscope; its design, construction and applications, held 

 by the Royal Microscopical Society, the Faraday Society, the Optical Society and 

 the Photographic Society in cooperation with the Technical Optics Committee of 

 the British Science Guild, in the rooms of the Royal Society, Jan. 14, 1920. The 

 papers and discussions at the Symposium, and the discussions since held in Sheffield 

 and Glasgow, and also a report of the discussion held in the Hall of the Royal 

 Microscopical Society in April. 1920, are soon to be published. 



CORNELL UNIVERSITY SIMON HENRY GAGE 



July 15, 1920 



