THE PRESIDEXt's ADDRESS. 189 



it is not enough to say tliat ' ' there are difficulties in the 

 projection and the calculation uncertain;" for he could never 

 be right in one case or the other. In a word, Brewster has no 

 claim whatever to be regarded as the author of an entoptical 

 method. 



But does it follow that if Brewster's claim be set aside, that 

 the whole credit is to be shared by Listing and Donders? I 

 have emphatically demurred to that by disenterring and, as far as 

 needful, reprinting in my Entoptics, a paper of mine on ' ' Points 

 in the Physiology and Diseases of the Eye," published in the 

 London Medical Gazette of May 9 and 16, 1845, about half of a 

 year before Listing's Beitrag appeared ; in which paper may be 

 found fully developed and geometrically diagramed and proved, 

 what are, in all essentials, both Listing's and Bonders' methods, — 

 that is, by one beam in relative lateral motion with the eye, and 

 by two beams with the eye and these relatively at rest. No 

 historian would assign any other date to Listing's claims than 

 the autumn of 1845, when they were first published to the 

 world, or allow the fact of some of his friends having been 

 making observations for him previously to be a plea for ante- 

 dating them, even though such observations had not been, as 

 they were, of such a kind that they might have been done 

 without any knowledge of his method, which might have been 

 an afterthought — not to mention that I had really commenced 

 with friends to observe for me in my observations, long before 

 he states himself to have done so. By all customar}^ rules 

 priority of publication of both said methods, however historians 

 had had it, belongs to me. 



Listing's motive in speaking of his friend's help was clearly 

 not to antedate his claims, and I do not for a moment imagine 

 that he got his idea from me. It is clear that Brewster had 

 not so got his : on the contrary, I might have derived the 

 thought of a couple of divergent beams from him. What mutual 

 knowledge we may have had of each other's essays I will briefly 

 tell, as I have a letter of his, which, now his fertile mind is lost 

 to us, and as it was in no way confidential, there may be no 

 impropriety in adducing, as it may be interesting in a bio- 

 graphical aspect as regards him. His paper was read only a 

 few weeks before my examination for a medical degree, on 



