THE place of illustration in book-making is found to vary through a wide range of values as one reviews a series of volumes at haphazard. In some the pages are flooded with pictures, from thumb-nail sketches on the margins to full-page prints in the natural colors of the original; in others page succeeds page in unbroken letter-press, without an illustration from cover to cover. Here, too, the picture is a true illustration of the text it accompanies; there it has scarcely more relation to the contents of the page it fronts than the engraving on a drawing-room wall bears to the volumes that may lie on a table before it. The significance of the picture, as an illustration, varies as much as, let us say, the artistic merit of its execution; and its value in any individual case may lie anywhere between zero and ideal adequacy.
The reasons for such fluctuation in the employment of illustration are of course legitimate as well as illegitimate. In one case, illustration may be indispensable, in another, inadmissable; the book-maker, whether author or publisher, is guided by the nature of his subject. In general, the material dealt with must be picturable if illustration is to be practicable. Only a small part of what the mind deals with in representative thought is thus picturable, and reflection itself is but one of the many interests which life comprises. To be presented in this spatial and visible manner the subject must be both concrete and material. Not all such subject-matter, indeed, can be successfully represented; but to conform to the conditions of picture-making it must at least fulfill these requirements.Much of our interest, both speculative and practical, falls outside this field of sensible reality. The relations and laws of things in the material world, for example, are abstractions which we formulate from the observation of a series of such individual concrete objects; and these abstractions, or generalizations, can not be represented pictorially, except figuratively, in a symbolic scheme. Such principles are aspects of the material world, though unpicturable; but there is another range of reality which does not offer itself to such treatment at all. Subjective experience has no sensible or representable content upon which to seize as the basis of an appeal to the eye. The absurdity of such a conception may be indicated by asking the shape of a thought, the color of anger, or the speed of a desire. When things belonging to this realm are writ-