Scientific observation tell us that living birds form a group or class of animals, through which a certain form of skeleton runs; and that this kind of skeleton differs in certain well-defined characters from that of mammals. On the other hand, if anyone utterly ignorant of osteology, but endowed with the artistic sense of form, were set before a bird skeleton and a mammalian skeleton, he would at once see that the two were similar and yet different. Very likely he would be unable to give clear expression to his just sense of the differences and resemblances; perhaps he would make great mistakes in detail if he tried. Nevertheless, he would be able to draw from memory a couple of sketches, in which all the salient points of likeness and unlikeness would be reproduced with sufficient accuracy. The mere osteologist, however accurately he might put the resemblances and differences into words, if he lacked the artistic visualising faculty, might be hopelessly incompetent to perform any such feat; lost in details, it might not even occur to him that it was possible; or, still more probably, the habit of looking for differences might impair the perception of resemblances. Under these circumstances, the artist might be led to higher and broader views, and thus be more useful to the progress of science than the osteological expert. Not that the former attains the higher truth by a different method; for the way of reaching truth is one and indivisible. Whether he knows it or not, the artist has made a generalization from two sets of facts, which is perfectly scientific in form; and trustworthy so far as it rests upon the direct perception of similarities and dissimilarities. The only peculiarity of the artistic application of scientific method lies in the artist's power of visualizing the result of his mental processes, of embodying the facts of resemblance in a visible "type," and of showing the manner in which the differences may be represented as modifications of that type; he does, in fact, instinctively, what an architect, who desires to demonstrate the community of plan in certain ancient temples, does by the methodical construction of plans, sections, and elevations, the comparison of which will furnish him with the "type" of such temples. Thus, what I may term the artistic fashion of dealing with anatomy is not only perfectly legitimate, but has been of great utility. The harm of it does not begin until the attempt is made to get more out of this visual projection of thought than it contains; until the origin of the notion of "type" is forgotten and the speculative philosopher deludes himself with the supposition that the generalization suggested by fact is an "Idea" of the Pure Reason, with which fact must, somehow or other, be made to agree. CCLXXXVIII