Architecture, sculpture and painting, because they are the three great arts which appeal to the spirit through the eye, are those too in which the sensible and the invisible meet with the strongest emphasis on themselves and yet the greatest necessity of each other. The form with its insistent masses, proportions, lines, colours, can here only justify them by their service for the something intangible it has to express; the spirit needs all the possible help of the material body to interpret itself to itself through the eye, yet asks of it that it shall be as transparent a veil as possible of its own greater significance.