CONTRIBUTIONS TO SCIENCE. 489 



a solution of chrome alum, the centre of the field of view 

 appears distinctly pink and much paler than the rest of 

 the solution on account of this peculiarity of the foramen 

 centmle. The effect decreases if the observer continue to 

 look. Maxwell's attention was first called to this peculiarity 

 of his own eye by noticing a black band in the blue portion 

 of the spectrum whenever he directed his eye straight to 

 that portion. The band never appeared in any other part 

 of the spectrum, but followed the eye up and down the 

 spectrum in the blue, vanishing as soon as the optic axis 

 passed out of the blue into other colours. 



The following account of Maxwell's explanation of 

 Haidinger's Brushes, and the personal reminiscences which 

 accompany it, have been kindly contributed by Professor 

 William Swan : 



My earliest noteworthy recollection of Clerk Maxwell dates 

 from 1850, when the British Association was in Edinburgh, and 

 its " Section A " used to meet in the natural philosophy class-room 

 of the University. That year communications were made by Sir 

 David Brewster and Professor Stokes on the remarkable pheno- 

 menon of vision discovered by Haidinger in 1844, and since 

 known as " Haidinger's Brushes." One day when a paper had 

 been read, which, if I remember rightly, was Brewster's, a young 

 man rose to speak. This was Clerk Maxwell. His utterance 

 then, most likely, would be somewhat spasmodic in character, as 

 it continued to be in later times, his words coming: in sudden 

 gushes with notable pauses between ; and I can well remember 

 the half-puzzled, half-anxious, and perhaps somewhat incredulous 

 air, with which the president and officers of the section, along 

 with the more conspicuous members who had chosen " the chief 

 seats " facing the general audience, at first gazed on the raw- 

 looking young man who, in broken accents, was addressing them. 

 For a time I was disposed to set down his apparent embarrass- 

 ment to bashfulness; and such, I daresay, was the general 

 impression. Bashful, very likely, in some degree he was. But, 

 at all events, he manfully stuck to his text ; nor did he sit down 

 before he had gained the respectful attention of his hearers, and 

 had succeeded, as it seemed, in saying all he meant to say. 



My only tolerably distinct further recollection is that he 

 handed in a small piece of apparatus which he had made by 

 cementing together on glass sectors of sheet gutta-percha, these 



