2 t THE ABC ,OF PHOTO - MICROGRAPHY 



slip of microscopic glass, and were used under 

 the microscope; being very favorite objects; 

 and always formed a portion of an amateur's 

 collection of slides. Their manufacture was 

 carried to great perfection in those days. I 

 have one made by Langenheim (a noted Phila- 

 delphia photographer), of the Lord's prayer, 

 which is so minute as to be invisible to the 

 naked eye. It requires a magnification of 

 nearly 100 diameters to be clearly read, under 

 which, each letter is sharply cut as though done 

 by the stroke of a pen, no granulation of the 

 silver being perceptible. It is a marvelous 

 piece of work, and probably could not be 

 duplicated at the present day. But to return. 

 By the same authority a Photo-Micrograph is 

 said to be " an enlarged photograph of a 

 microscopic object produced by throwing its 

 image through a suitable combination of micro- 

 scope and camera." It is the latter class that 

 forms the subject matter of this little volume, 

 and by this means the negatives were made 

 from which the reproductions that illustrate it 

 were produced. My friend, Dr. A. Clifford 

 Mercer, has given probably the most concise 

 definitions of the two terms. He says " a 

 micro-photograph is a microscopic photograph 

 of a macroscopic object. A photo-micrograph 



