406 



Mr. E. Wilson on a remarkable Alteration March 21, 



The author then adverts to the suspicion of inaccuracy in some parts of 

 these results, arising from the circumstance that KirchhofF's apparatus 

 was not always in precisely the same state of adjustment. After expressing 

 his own a priori belief that the error, if any, must be extremely small, he 

 adverts to the comparison which he was now enabled to make between 



o 



direct measures of wave-length by Angstrom and Ditscheiner, and his own 

 computations. Admitting the systematic errors of Frauuhofer which the 

 later philosophers have indicated, and the errors incidental to interpolation 

 and extrapolation, the remaining discrepance is very small. Its progress is 

 so easy that there is no difficulty in interpolating its value for any one 

 line; and thus, using the computed wave-lengths of this memoir, the 

 wave-length for any line may be found as it would have been measured by 

 Angstrom or Ditscheiner. 



In the tabular part of the communication, the principal Table contains 

 KirchhofF's measures and symbols, extracted from the Berlin Memoirs 

 1861 and 1862, with the addition throughout of one column containing the 

 author's computed wave-lengths expressed in parts of the millimetre. This 

 is followed by a special Table, in the same form, for the lines produced by 

 certain metals not included in the general Table. There is then given a 

 Table of the wave-lengths corresponding to the lines produced by different 

 metals, extracted by the author from the general Table. And finally there 

 are given two Tables containing respectively the comparisons of Angstrom's 

 and Ditscheiner's direct measures of wave-lengths with the wave-lengths 

 computed by the author. 



II. "On a remarkable Alteration of Appearance and Structure of 

 the Human Hair.^' By Erasmus Wilson, E.R.S. Received 

 March 12, 1867. 



I have the honour of submitting to the Royal Society a specimen of 

 human hair of very remarkable appearance. Every hair is brown and 

 white in alternate bands, looking as if encircled with rings ; and this 

 change of aspect extends throughout the whole length of the hair, and 

 gives to the general mass a curiously speckled character. The brown 

 segment of the hair, which represents its normal colour, measures about 

 of an inch in length, or something less than a quarter of a line ; the 

 white, or abnormal segment about half that length, namely 

 inch ; and the two together about of an inch, or one-third of a line. 



The hair was taken from a lad aged seven years and a half, a gentle- 

 man's son; he is reported as being "an active, healthy boy, quick and 

 intelligent." He was delicate up to the age of four, having suffered in 

 quick succession the diseases of childhood, a severe attack of croup, and 

 several attacks of convulsions. The change in the appearance of the hair 

 was first noticed when he was between two and three years old, and has 



