Walter Frank Raphael Weldon. 1860—1906. 17 
" On certain correlated Variations in Crangon vulgaris" (14), Weldon calculated the 
first coefficients of organic correlation, i.e. the numerical measures of the degree of 
interrelation between two organs or characters in the same individual. It is quite 
true that the complete modern methods were not adopted in either of these 
papers, but we have for the first time organic correlation coefficients — although 
not yet called by that name — tabled for four local races. These two papers are 
epoch-making in the history of the science, afterwards called biometry. 
It is right to state that Weldon's mathematical knowledge at this period was 
far more limited than it afterwards became. The first paper was sent to Francis 
Galton as referee, and was the commencement of a life-long friendship between 
the two men. With Galton's aid the statistical treatment was remodelled, and 
considerable modifications made in the conclusions. But the credit of making 
the vast system of measurements, of carrying out the necessary calculations (now 
with the aid of his wife, who was for years to assist in this part of the work), of 
seeing a priori the bearing of his results on the great problems of evolution, must 
be given to Weldon. Nor must we forget the rich suggestiveness of these papers. 
Weldon was on the look-out for a numerical measure of species. He was seeking 
for something constant for all local races, and although his suggestion that the 
correlation coefficient was a constant for local races has not been substantiated — 
the " selection constant," the quantity uninfluenced by racial diffei'entiation, 
being of a much more complex nature — yet his suggestion directly led up to the 
investigation of correlation in man, animals and plants, and has given us immensely 
clearer ideas on the inter-relationship of organic characters. And Weldon realised 
this also : 
"A large series of such specific constant.? would give an altogether new kind of knowledge of 
the physiological connexion between the various organs of animals ; while a study of those 
relations which remain constant through large groups of species would give an idea, attainable 
in no other way, of the functional correlations between various organs which have led to the 
establishment of the great sub-divisions of the animal kingdom*." 
The defect in mathematical grasp, which Weldon had realised in his first 
paper, led him at once to seek to eliminate it. He sought first to ' enthuse ' a 
mathematician with his project of demonstrating Darwinian evolution by statistical 
enquiries. A visit was paid to Cambridge with this end in view, but it did not 
lead to the required result. Weldon then set about increasing his mathematical 
knowledge by a thorough study of the great French writers on the calculus of 
probability. He did not turn to elementary text-books but with his characteristic 
thoroughness went to the fountain head. Turning over his papers now, it is 
astonishing to notice the completeness of his studies as evidenced by his notes 
and abstracts. He thus attained to a very great power of following mathematical 
reasoning and this power developed with the years. He never reached a high 
wrangler's readiness in applying analysis to the solution of new questions, possibly 
this requires years of training in problem papers ; but he was able to follow and 
* R. S. Proc. Vol. LI. p. 11. 
Biometrika v 3 
