194 THE pbesident's ADDE,E"SS. 



In tlie application of this narrative to what has been said 

 before on the discrepancies of history, I mnst call attention to 

 the fact that Helmholtz' preface to his work is dated in December 

 1866, and that its supplementary chapter on " Entoptical 

 Phenomena" is so close to the end as to be preceded by many 

 references to the literature of that year. Nevertheless, a book 

 had been in existence since the Spring of 1864, which remoulds 

 the subject in such a manner as scarcely to leave one of his 

 paragraphs thereon unaffected, and is often (as exemplified in 

 the vitreous humour) subversive of the conclusions he has 

 adopted, besides furnishing many that he nowhere indicates ; 

 and though he is familiar with the language in which it is 

 written, and that his own countrymen had been emphatically 

 apprized of its tenour in their own, yet there is no sign that he 

 had ever heard of it ! It is of no avail that he chronicles a couple 

 of papers of mine (with an erroneous statement not, apparently, 

 from his own reading, as to the aim of one of them) which by 

 the side of my first essay in 1845 and my last in 1864, are of 

 slight moment in the history of entoptics. These incidents 

 combine in displaying how much the celebrated Heidelberg 

 professor of physiology, in the turmoil of his multitudinous 

 scientific researches and avocations, deceived himself in imagining 

 that the time he had spent in looking up or through other persons 

 writings was enough to keep him abreast of the later contri- 

 butions to physiological optics in all its sections. 



In a historical point of view the fate of my paper of 1845 is 

 curious. We have seen with what nonclialance Brewster threw 

 it aside. Mackenzie, who was our only systematic chronicler of 

 entoptical writings, barely gives it mention with its date (omitting 

 its title) in his bibliographical list, among such writings as are 

 there said to treat on '' methods of examining spectra." Of 

 course, he saw it through Brewster's spectacles. The Gazette in 

 which it appeared would hardly bring it under Listing's notice. 

 Up to the time of the publication of his "Anomalies," (Brew- 

 ster's essay excepted) Bonders had no other acquaintance with 

 English productions on the subject than what he could glean 

 from Mackenzie's work on Diseases of the Eye. Helmholtz 

 omitted to consult, directly, such literature altogether. In a 

 word the paper had never been read by any unprejudiced and 

 competent entoptical investigator, and had I not, many years 



