PREFACE, 
V. 
Sir W. J. Dawson, speaking as the President of the 
British Association, at Birmingham, said :— 
“ It is impossible for any man to keep pace with the progress of 
more than one limited branch of science, and it is equally impossible 
to find an audience of scientific men of whom anything more than a 
mere fraction can be expected to take an interest in any one subject.” 
And as in the region of experiment and observation each 
man may set himself to cultivate his own department, why 
may not some men devote themselves to the discussion of 
theories—to that branch of science which consists in putting 
the right interpretation on the phenomena which have been 
observed and chronicled? When Mr. Galton, in consider 
ing a certain problem, referred to a mathematician to work 
the result from certain elements that were supplied, he 
took for granted the ability of the mathematician within 
his own sphere, and did not depreciate his part of the 
work because he was not an expert in physical or 
biological science. 
But perhaps it will be said that it is impossible that the 
man who is not an expert in a particular branch, should 
understand anything about it. Nevertheless, in the 
address just quoted, Sir W. J. Dawson goes on to express 
a hope that the specialist can make himself understood :— 
“ There is, however, some consolation in the knowledge that a 
speaker who is sufficiently simple for those who are advanced 
specialists in other departments will, of necessity, be also sufficiently 
simple to be understood by the general public who are specialists in 
nothing.” 
And indeed it would be strange if the proof of principles 
or the statement of definite and special facts could not be 
made intelligible, and could not be submitted to the judg 
ment of the general public. The command to every 
thinker, who is not a specialist—Go to a biological