vi PREFACE. 



service it has rendered, the fact has not been lost sight of that the microscope is, 

 after all, only an aid to the eye of the observer, only a means of getting a larger 

 image on the retina than would be possible without it ; but the appreciation of tbis 

 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 appreciating brain 

 behind the eye. The microscope simply aids the eye in furnishing raw material, 

 so to speak, for the brain to work upon. 



"The necessity for doing a vast deal of drudgery, or 'dead work,' as it has been 

 happily styled by Professor Leslie, before one has the training necessary for the 

 appreciation and the production of original results, has been well stated by Beale : 



"'The number of original observers emanating from our schools will vary as 

 practical work is favored or discouraged. It is certain that they who are most 

 fully conversant with elementary details and most clever at demonstration, will be 

 most successful in the consideration of the higher and more abstruse problems, 

 and will feel a real love for their work which no mere superficial inquirer will ex- 

 perience. It is only by being thoroughly grounded in first principles, and well 

 practiced in mechanical operations, that any one can hope to achieve real success 

 in the higher branches of scientific enquiry, or to detect the fallacy of certain so- 

 called experiments.' " 



SIMON HENRY GAGE, 

 Cornell University, 



February 12, i8g{. Ithaca, New York, U. S. A. 



