LITERATURE OF THE MICROSCOPE 211 



Books on the Theory of the Microscope. — With regard 

 to the theory of the microscope, the most imi)ortant work 

 of general interest is, of course, the first volume of Abbe's 

 collected papers. Here we have a man of genius bending 

 his energies to the improvement of the microscope. These 

 papers are semipopular, in that mathematics is almost 

 wholly omitted. Abbe's mathematical discoveries are 

 given in the books of Czapski, von Rohr et al., and Lum- 

 mer. All Abbe's papers are important, but perhaps the 

 most interesting are the original account of the diffraction 

 theory (2); the reply to an attack on his theory (11); 

 the theory of binocular vision (10, 12) ; the descriptions of the 

 invention of the oil-immersion objective (6, 7), and of the 

 apochromatic objectives (17) ; and the study of the proper 

 focal length for objectives of different apertures (14). The 

 writer owes his interest in scientific microscopy mainly to 

 the reading of these papers. Dippel's book (60), except as 

 a record of the state of microscopical affairs in Germany 

 before 1882, is chiefly valuable for Abbe's account of his 

 theory, which he gave to Dippel for insertion. The new 

 edition (1924) of Czapski's book on the theory of optical 

 instruments after Abbe (57), contains an excellent com- 

 pressed, more or less mathematical, account of the micro- 

 scope (as well as of other optical instruments). The 

 interesting chapters for our purpose are V, XI, XII, XIII, 

 XV, XVI and XIX. One may find in this work a good 

 account of microscopical calculations, and also a very 

 complete bibliography of optical discovery. Koehler's 

 treatise on the hand lens and the simple microscope (86) 

 is a full and elegant theoretical exposition, containing 

 many points of interest. It would be useful to have the 

 compound microscope treated in a similarly full theoretical 

 manner. 



Papers on Large Cones. — Among the important articles on 

 the microscope since Abbe's time are the following on large 

 cones of illumination: Nelson, in the Journal of the Royal 

 Microscopical Society (101) and in the Eriglish Mechanic, 

 upheld his well-known method of critical illumination. 



