extreme, which eventually became only less deleterious to the interests of science than was the bondage of authority, and addiction to a priori methods, from which the revolt had set her free. For, without here waiting to trace the history of this matter in detail, I think it ought now to be manifest to everyone who studies it, that up to the commencement of the present century the progress of science in general, and of natural history in particular, was seriously retarded by what may be termed the Bugbear of Speculation. Fully awakened to the dangers of web-spinning from the ever-fertile resources of their own inner consciousness, naturalists became more and more abandoned to the idea that their science ought to consist in a mere observation of facts, or tabulation of phenomena, without attempt at theorizing upon their philosophical import. If the facts and phenomena presented any such import, that was an affair for men of letters to deal with; but, as men of science, it was their duty to avoid the seductive temptations of the world, the flesh, and the devil, in the form of speculation, deduction, and generalization.

I do not allege that this ideal of natural history was either absolute or universal; but there can be no question that it was both orthodox and general. Even Linnæus was express in his limitations of true scientific work in natural history to the collecting and arranging of species of plants and animals. In accordance with this view, the status of a botanist or a zoologist was estimated by the number of specific names, natural habitats, &c., which he could retain in his memory, rather than by any evidences which he might give of intellectual powers in the way of constructive thought. At the most these powers might legitimately exercise themselves only in the direction of taxonomic work; and if a Hales, a Haller, or a Hunter obtained any brilliant results in the way of observation and experiment, their merit was taken to consist in the discovery of facts per se: not in any endeavours they might make in the way of combining their facts under general principles. Even as late in the day as Cuvier this ideal was upheld as the strictly legitimate one for a naturalist to follow; and although Cuvier himself was far from being always loyal to it, he leaves no doubt regarding the estimate in which he held the still greater deviations of his colleagues, St. Hilaire and Lamarck.

Now, these traditional notions touching the severance between the facts of natural history and the philosophy of it, continued more or less to dominate the minds of naturalists until the publication of the Origin of Species, in 1859. Then it was that an epoch was marked in this respect, as in so many other respects where natural history is concerned. For, looking to the enormous results which followed from a deliberate disregard of such traditional canons by Darwin, it has long since become impossible for naturalists, even of the strictest sect, not to perceive that their previous bondage to the law of a mere ritual has been for ever superseded by what verily deserves to be regarded as a new dispensation. Yet it cannot be said, or even so much as suspected, that Darwin’s method in any way resembled that of pre-scientific days, the revolt against which led to the straight-laced—and for a long time most salutary—conceptions of method that we have just been noticing. Where, then, is the difference? To me it seems that the difference is as follows; and, if so, that not the least of our many obligations to Darwin as the great organizer of biological science arises from his having clearly displayed the true principle which ought to govern biological research.

To begin with, he nowhere loses sight of the primary distinction between fact and theory; so that, thus far, he loyally follows the spirit of revolt against subjective methods. But, while always holding this distinction clearly 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 constitute the final aim of scientific research, obviously the advancement of such research can be attained only by the framing of hypotheses. And to frame hypotheses is to speculate.

Therefore, the difference between science and speculation is not a difference of spirit; nor, thus far, is it a difference of method. The only difference between them is in the subsequent process of verifying hypotheses. For while speculation, in its purest form, is satisfied to test her explanations only by the degree in which they accord with our subjective ideas of probability—or with the “Illative Sense” of Cardinal Newman,—science is not satisfied to rest in any explanation as final until it shall have been fully verified by an appeal to objective proof. This distinction is now so well and so generally appreciated that I need not dwell upon it. Nor need I wait to go into any details with regard to the so-called canons of verification. My only object is to make perfectly clear, first, that in order to have any question to put to the test of objective verification, science must already have so far employed the method of speculation as to have framed a question to be tested; and, secondly, that the point where science parts company with speculation is the point where this testing process begins.

Now, if these things are so, there can be no doubt that Darwin was