VI PERSISTENCE 9 5
colour sense and therefore hardly able, if at all, to distinguish even the blue numerals in Figs. 20, 21, I give an eleventh example, Plate 15, Fig. 22, printed all in black. The numerals are here very legible, but space for their insertion had to be obtained by sacrificing some of the lineations. It is the right fore-finger of Sir W. Herschel and has been already published twice ; first in the account of my lecture at the Royal Institution, and secondly, in its present conspicuous form, in my paper in the Nineteenth Century. The number of years that elapsed between the two impressions is thirty-one, and the prints contain twentyfour points of comparison, all of which will be seen to agree. I also possess a later print than this, taken in 1890 from the same finger, which tells the same tale.
The final result of the prints in these pages is that they give photographic enlargements of the whole or portions of eleven couplets belonging to six different persons, who are members of five unrelated families, and which contain between them 158 points of comparison, of which only one failed. Adding the portions of the prints that are omitted here, but which will be found in the Phil. Trans., the material that I have thus far published contains 389 points of comparison, of which one failed. The details are given in the annexed table
[TABLE
