Before, however, we enter upon any one of these it is right that we remind the reader--and remind him once for all--that our knowledge upon all these points is but partial and uncertain, and never of such a character as will allow us to speak with dogmatic assurance. Our information can necessarily never be direct; it can only be built upon inferences of a higher or lower degree of probability. It is, however, a necessity of our minds that from whatever information we possess we must form an unbroken panorama--imagination has no place for unfilled blanks; and we may form our picture freely and without danger of harm, so long as we are ready to modify or enlarge it when more knowledge is forthcoming. As the eye can in a moment supply the deficiencies of some incompleted picture, a landscape of which it gets only a partial glance, or a statue which has lost a feature, so the mind selects from its knowledge those facts which form a continuous story, and loses those which are known only as isolated fragments. Set a practised and an unpractised draughtsman to draw a circle, and we may witness how differently they go to work. The second never takes his pencil off the paper, and produces his effect by one continuous line, which the eye has no choice but at once to condemn as incomplete. The wiser artist proceeds by a number of short consecutive strokes, splitting up, as it were, his divergence over the whole length of the figure he is drawing, and so allows the eye, or perhaps one should rather say the mind, by that faculty it has, to select the complete figure which it can conceive more easily than express. No one of the artist’s strokes is the true fraction of a circle, but the result is infinitely more satisfactory than if he had tried to make his pencil follow unswervingly the curve he wished to trace. Or again, notice how a skilful draughtsman will patch up by a number of small strokes any imperfect portion of a curve he is drawing, and we have another like instance of this selective faculty of the eye or of the mind. Just in the same way is it with memory. Our ideas must be carried on continuously, we cannot afford to remember _lacunæ_, mere blank spaces.