JOURNAL 



OF THE 



ROYAL MICROSCOPICAL SOCIETY. 



AUGUST 1901. 



TRANSACTIONS OF THE SOCIETY. 



VII. — An Examination of the Abbe Diffraction Theory of the 



Microscope. 



By J. W. Gordon. 



(Bead June 19, 1901.) 



Plate VII. 



The Abbe theory, which I have this evening the honour to bring under 

 discussion in your assembly, stands in the very curious position of 

 having attained to general acceptance without having ever been 

 proved, and of being commonly received on the authority of its author, 

 who has in terms repudiated it. For my own part I should have 

 preferred, had that been possible, to discuss the theory in the abstract 

 without connecting it with any person, because of the risk which the 

 introduction of the author's name involves of giving to the discussion 

 itself a personal character, and so substituting barren altercation for 

 useful debate. But the hypothesis in question has been so long and 

 is so widely known as the Abbe theory, that it would be idle for me to 

 avoid the use of Professor Abbe's name for the purpose of identifying 

 it. But it will, I hope, be recognised that I make no attack upon 

 Professor Abbe himself ; I do not even attribute to him the champion- 

 ship of the theory which goes by his name, and which appears to me 

 to be propagated at the present time by his disciples rather than by 

 himself. And lest I should, by inadvertence, do him any injustice, 

 I desire your leave to place in the forefront of my criticisms the 

 disclaimer of the Abbe theory which Professor Abbe has himself 

 published. 



The disclaimer is to be found in the 7th edition of Carpenter's 

 The Microscope and its Eevelations, at p. 64, where an extract is 

 given from a letter in which Professor Abbe says : — 



" I no longer maintain in principle the distinction between the 

 ' absorption image ' (or direct dioptrical image) and the ' diffraction 

 Aug. 21st, 1901 2 b 



