THE president's ADDRESS. 183 



entoptical characteristics of the lens which he was about to 

 define was derived from observations of his own, which had 

 been pursued for about two years and a half, and from others 

 of friends that had, in "many" instances, been extended over 

 a year. The second gives from p. 58, a definition of these 

 characteristics. To the latter of these I had no motive in 

 making, and did not make a textual reference : but to the 

 original text of the former, I thought it incumbent on me to 

 refer, because the Beitrag contains a fundamental principle 

 of entoptics, which, as I contemplated showing in the sequel, 

 had been expounded in a paper of mine more than a half of a 

 year before its appearance ; and I would not have it supposed 

 that I would be reticent as to a statement that might be thought 

 by any one to have weight in a question of priority of publication 

 in which I was concerned. Nevertheless (a fact that I must ask 

 you to note) my good intentions as to the reference have been 

 marred by a misprint, by which, instead of to p. 47, the reader 

 is directed to p. 17, at which earlier part of the Beitrag totally 

 different matter is treated of. Finally, — to show how this nar- 

 rative bears upon the pamphlet presented to me, — its definition 

 of the entoptic figure of the crystalline lens as taken from 

 Listing's Beitrag is couched in language only slightly varied in 

 phrase from that of my translation of the passage from p. 58 ; 

 yet it is not from that page the author cites it, but, mirahile dictu, 

 from p. 17, exactly according with the misprint in my book ! 

 This untoward coincidence is intelligible on the assumption that 

 the drift of my reference had been misapprehended to apply to 

 the subject matter instead of to an interval of time, and that the 

 author, in default of having read the Beitrag himself, evolved his 

 version of a portion of its contents from the said source, and 

 such other hints in the English language — whether printed, 

 written, or conversational — as he confessedly had at his command. 

 Otherwise it would be a recondite problem in the doctrine of 

 probabilities. 



The samples I have here submitted of irregularities in the 

 transcription of texts and avowals of literary obligations, though 

 drawn solely from my own limited experience, suffice to convey 

 some idea of the range of such occurrences, if only an imperfect 

 one of their diversity. 



