428 The Evolution of Scientific Knowledge. [July, 
how Chemistry has aided electrical science, and been aided 
in turn by that science ; we have only to observe how 
Geology has profited by the advance of Biology, and at the 
same time has aided in solving important biological pro- 
blems ; we have only, in a word, to study the history of 
Science in a scientific spirit, to see how completely the 
organs of the body scientific are dependent on each other, 
and are bound together into a definite complex whole. 
Let it then be clearly noted that the advance in scientific 
knowledge is not merely, as some suppose, an increase of 
the mass of accumulated fadts. It is this, but it is much 
more besides. Just as the more extended view which the 
mountaineer obtains as he rises above the valley does not 
charm so much by the multiplicity of objedts as by the 
connedtion which is disclosed among them, so, too, the 
more extended view which the philosopher obtains, as he 
climbs the hill of Science, does not owe its value so much 
to the number of fadts accumulated as to their definite 
organisation. 
In conclusion, one or two general .fadts may be pointed 
out. There is no more striking trait in the evolution of 
knowledge than the fadt that not unfrequently the same 
discovery is made almost simultaneously by different workers 
labouring altogether independently of each other. Instance 
the theory of Natural Seleftion elaborated simultaneously by 
Darwin and Wallace ; instance, again, the independent lique- 
fadtion of oxygen by MM. Pidtet and Cailletet. Or again, 
perhaps, we find that the same law or theory is advanced by 
several men as a speculation, and by one master mind as a 
demonstration. This may be said to have been the case in 
the discovery of the Law of Universal Gravitation. Now 
these fadts are in full accordance with the theory that the 
development of our knowledge is an evolution. When the 
environment of ascertained fadt has reached a certain defi- 
nite state, its influence inevitably calls forth the development 
of a new theory which shall be in harmony with all the 
conditions. In the minds of Newton’s contemporaries the 
environment of accumulated fadts called forth general con- 
ceptions more or less in harmony with these fadts ; but in 
the master mind of Newton not only was the enviionment 
of fadt more extended, from his powerful grasp of intelledt, 
not only was that environment more pressing, from, his 
constant habit of earnest thought, — but the conceptions 
were more definite, from the extraordinary depth of his 
mathematical insight. The result was the produdtion of a 
law and a book which have been the wonder of all after-time. 
