iv PREFACE 



the retinal image, whether it is made with or without the aid of a microscope, 

 must always depend upon the character and training of the seeing and appreciat- 

 ing brain behind the eye. The microscope simply aids the eye in furnishing raw 

 material, so to speak, for the brain to work upon. (From 3d ed. ) 



Grateful acknowledgment is made to the opticians and instrument makers 

 for the loan of cuts and for courteous and complete answers to numerous question ; 

 to the directors of laboratories in different parts of the country, to his colleagues 

 in the departments of Physics, Chemistry and Electrical Engineering in Cornell 

 University; and finally to his pupils past and present wbo have given their sup- 

 port and encouragement. 



In closing I would like to urge those who are interested in Microscopy to 

 take same microscopical journal, and if possible to become a member of some 

 microscopical club or society. One can do very little alone, but by helping others 

 and being helped in return, the workers in any field of human endeavor can 

 accomplish great things. 



SIMON HENRY GAGE, 

 Cornell University, 



October /, /go/. Ithaca, N. Y., U. S. A. 



