250 MEMORIES OF MY LIFE 



head, though low, but after all it was not so very 

 large in circumference. Of those persons whom I 

 have mentioned in the foregoing chapters, the heads 

 of William Spottiswoode and Mr. Gassiott were 

 larger round ; Professor Sharpey's was the largest of 

 all. A slight want of symmetry on which Mr. 

 Gladstone laid stress was no peculiarity at all, for the 

 heads of normal persons are rarely quite symmetrical. 



The " Measurement of Resemblance'^ between 

 portraits is a subject on which I have been engaged off 

 and on during late years, and which I hope to take up 

 again. The best of my ideas at present is to prepare a 

 strip of card one inch broad and printed with numerals 

 of various standard sizes from i to 9. Then to mount 

 the portraits on slides actuated by strings, and to 

 station them at such distances that the interval between 

 the pupils of the eyes and the mouth in each portrait 

 shall be apparently the same as the breadth of the 

 strip. Then to interpose a wedge of tinted glass in 

 front of an eye-hole, and to slide it until the portraits 

 become indistinguishable. In that position to read 

 off the smallest of the standard numbers that is 

 simultaneously legible. I have made many experi- 

 ments, differing in particulars, and described one of 

 them in Nature, October 4, 1906 [175], which 

 seems to me not so good as the one briefly outlined 

 above. 



The chief value to me of the Laboratory during 

 the latter part of the time of its existence, and the 

 reason why I continued it so long, lay in the con- 

 venience it afforded for obtaining and testing the 

 value of finger-prints. My interest in them arose 

 through a request to give a Friday evening lecture 



