42 ? 
1880.J The Evolution of Scientific Knowledge . 
which law, considered as it is by some the chief glory of 
modern science, exemplifies clearly the results of an evolu- 
tion. As a quantitative law it has increased the definiteness 
of our knowledge ; as a generalisation which comprehends 
all forms of energy, it has increased the integration of our 
knowledge ; and, implying as it does the transformations of 
the various forms of energy into each other, it exemplifies 
also an increase in dependence and orderly harmony. 
Having now given some examples of the evolution of 
certain branches of scientific knowledge (lack of space pre- 
cluding further exemplification from the biological, socio- 
logical, and psychological sciences), the faCt must be pointed 
out that in no case is the evolution of one branch of such 
knowledge independent of the evolution of other branches. 
The term branchy indeed, suggests the conception of a 
general tree of knowledge of which they are the offshoots. 
But the special sciences might perhaps be more profitably 
likened to the organs of the animal organism. For not 
only do the several organs progress together with the pro- 
gress of the whole of which they are the parts, but each 
organ ministers in its own fashion to the welfare of the 
whole and of the other organs. Mr. Herbert Spencer has 
given many examples of the dependence of the advance of 
one branch of science upon the advance of other branches. 
It is therefore unnecessary here to do more than indicate 
the nature of the evidence. Where would Astronomy be 
now, it may be asked, without the advance in Optics implied 
in achromatic telescopes ; without the discoveries in Me- 
chanics of the laws of motion, and of the anachronism of 
the pendulum ; without the determination of the specific 
gravity of the earth, and the measurement of a degree on 
the earth’s surface ? There is indeed scarcely a branch of 
Science upon which Astronomy does not call for aid. In 
addition to those just mentioned she relies on Atmospheric 
Physics for tables of atmospheric refraction ; upon Chemistry 
for photographic processes ; upon Electricity for various re- 
cording instruments ; and upon Psychology for the personal 
equation, — the time which elapses between seeing and regis- 
tering which varies in different individuals. These fads are 
sufficient to exemplify the inter-dependence of the sciences, 
and they form not a tithe of the number which could be 
adduced. We have only to trace the interaction of terres- 
trial and astronomical physics on Mathematics, to watch 
how new problems in physics called forth new mathematical 
processes, which processes enabled further physical advance, 
and thus led to fresh problems ; we have only to consider 
