y in view, his idea of the scientific use of facts is
plainly that of furnishing legitimate material for the construction of
theories. Natural history is not to him an affair of the herbarium or
the cabinet. The collectors and the species-framers are, as it were, his
diggers of clay and makers of bricks: even the skilled observers and the
trained experimentalists are his mechanics. Valuable as the work of all
these men is in itself, its principal value, as he has finally
demonstrated, is that which it acquires in rendering possible the work
of the architect. Therefore, although he has toiled in all the trades
with his own hands, and in each has accomplished some of the best work
that has ever been done, the great difference between him and most of
his predecessors consists in this,--that while to them the discovery or
accumulation of facts was an end, to him it is the means. In their eyes
it was enough that the facts should be discovered and recorded. In his
eyes the value of facts is due to their power of guiding the mind to a
further discovery of principles. And the extraordinary success which
attended his work in this respect of _generalization_ immediately
brought natural history into line with the other inductive sciences,
behind which, in this most important of all respects, she has so
seriously fallen. For it was the _Origin of Species_ which first clearly
revealed to naturalists as a class, that it was the duty of their
science to take as its motto, what is really the motto of natural
science in general,

Felix qui potuit rerum cognoscere causas.

Not facts, then, or phenomena, but causes or principles, are the
ultimate objects of scientific quest. It remains to ask, How ought this
quest to be prosecuted?

Well, in the second place, Darwin has shown that next only to the
importance of clearly distinguishing between facts and theories on the
one hand, and of clearly recognising the relation between them on the
other, is the importance of not being scared by the Bugbear of
Speculation. The spirit of speculation is the same as the spirit of
science, namely, as we have just seen, a desire to know the causes of
things. The _hypotheses non fingo_ of Newton, if taken to mean what it
is often understood as meaning, would express precisely the opposite
spirit from that in which all scientific research must necessarily take
its origin. For if it be causes or principles, as distinguished from
facts or phenomena, that