As it must first be a caterpillar, and devour greedily leaf, fibre, and all that can be devoured by caterpillars, so the student must settle down and devour all the knowledge that he can find, and crawl slowly along unheeded, or be looked at perhaps with contempt. As it changes its skin many times while growing, so must he change the style of his admiration. As it carries within it the wings and the colours in the egg state, so the light wings of fancy and the pure instinct of colour must be born in the painter, or it cannot be altogether trained: a perception which, like the perception of music, will cause his nerves to quiver at a discordancy, although he never handled a brush. 'Full many a poet never penned a line,' and so with the painters who have lived and died with their dreams unchronicled, the perception being too fine for the material contact of earth, which must pollute, even while it embodies; a perception ever running before the knowledge, ever torturing the possessor with the innate consciousness of his errors before he has learnt enough to perceive them. Form is the grammar of art--a thing of measurements, which can be tested, corrected, and satisfied by the exact laws which govern it; but colour is too fitful a possession to be tested or controlled by rule or education beyond a certain stage. We have it when we least expect it, and find it slipping from our grasp, after a life-long experience renders us confident of its control. It is a quality far too subtle to be described by words; a sensitive gift which will torture the gifted, as George Paul Chalmers, the Scottish Rembrandt, was tortured until his spirit became unnerved with the galling longing, and his brush blundered and would not finish. It is not the wings of the butterfly but the golden dust which covers them, and which is so easy to rub away; not the genius of the painter, but the precious garment of his genius, to which genius is as much indebted as her mortal sisters are to the costumes of a more terrestrial texture; too fine a fabric for earth looms to spin, too delicate to be measured or shaped by fashion; and even as the caterpillar must suffer the throes and self-efforts of Nature, and lie under the wearied languor of spent exertion, so must the student painter torture and weary his heart out with his many struggles to do that which his instinct tells him must be. Many caterpillars perish from their own efforts, many are destroyed by enemies, many are killed by their own kind; and how like is all this experience to that of the student painter!