267 



On True versus False Images in Microscopy. 



By T. F. Smith. 

 (Bead May 2oth, 1888.) 



The object of my paper to-night is to endeavour to help clear 

 away the doubt about what may be accepted as a true interpreta- 

 tion of microscopic structure. To myself the subject presents no 

 difficulty whatever, believing, as I do, that with proper illumina- 

 tion the image may be absolutely depended upon ; but I cannot, 

 in the face of all that has been written to the contrarv, and 

 especially in reference to the extraordinary paper in the last 

 February number of the " Journal of the Royal Microscopical 

 Society " on " Histological Structure and the Diffraction Theory," 

 be blind to the fact that the minds of many microscopists are in 

 a state of chaos as to what they may accept and what reject of 

 the image presented to the eye. I admit it requires a certain 

 amount of courage to believe the evidence of one's own eyes, 

 when so eminent an authority as Dr. Abbe tells us it is impossible 

 the microscope can give a correct image under the circumstances ; 

 but great as may be mathematics, great also is common sense, 

 and, as far as I am concerned, when the image I look at tells me 

 it is the only possible interpretation of the structure, I am bound 

 to believe it. 



In the October and November numbers of the " Monthly 

 Microscopical Journal ' for 1875, appear some extracts from 

 Mr. Fripp's translation of Dr. Abbe's " Paper on the Microscope," 

 which translation gave for the first time in English an account 

 of the celebrated " Diffraction Theory." In it Dr. Abbe teaches that 

 while the parts of an object not exceeding in size the 2-3-V0 part 

 of an inch are imaged geometrically, and consequently an exact 

 counterpart of the object, the delineation of the finer structure 

 is due to the diffraction of light, and is, as a rule, not imaged 

 conformably with the actual constituent detail of the object itself. 

 In giving examples, he says that it is impossible to determine the 

 structure of the finer kinds of diatoms from their microscopical 

 appearance. " Whether, for instance, Pleurasigma angulation 



