The Stones of Venice, Volume 1 (of 3)

by John Ruskin

§ VI. Now the arch line is the ghost or skeleton of the arch; or rather it is the spinal marrow of the arch, and the voussoirs are the vertebræ, which keep it safe and sound, and clothe it. This arch line the architect has first to conceive and shape in his mind, as opposed to, or having to bear, certain forces which will try to distort it this way and that; and against which he is first to direct and bend the line itself into as strong resistance as he may, and then, with his voussoirs and what else he can, to guard it, and help it, and keep it to its duty and in its shape. So the arch line is the moral character of the arch, and the adverse forces are its temptations; and the voussoirs, and what else we may help it with, are its armor and its motives to good conduct.

§ VII. This moral character of the arch is called by architects its “Line of Resistance.” There is a great deal of nicety in calculating it with precision, just as there is sometimes in finding out very precisely what is a man’s true line of moral conduct; but this, in arch morality and in man morality, is a very simple and easily to be understood principle,—that if either arch or man expose themselves to their special temptations or adverse forces, outside of the voussoirs or proper and appointed armor, both will fall. An arch whose line of resistance is in the middle of its voussoirs is perfectly safe: in proportion as the said line runs near the edge of its voussoirs, the arch is in danger, as the man is who nears temptation; and the moment the line of resistance emerges out of the voussoirs the arch falls.

§ VIII. There are, therefore, properly speaking, two arch lines. One is the visible direction or curve of the arch, which may generally be considered as the under edge of its voussoirs, and which has often no more to do with the real stability of the arch, than a man’s apparent conduct has with his heart. The other line, which is the line of resistance, or line of good behavior, may or may not be consistent with the outward and apparent curves of the arch; but if not, then the security of the arch depends simply upon this, whether the voussoirs which assume or pretend to the one line are wide enough to include the other.

§ IX. Now when the reader is told that the line of resistance varies with every change either in place or quantity of the weight above the arch, he will see at once that we have no chance of arranging arches by their moral characters: we can only take the apparent arch line, or visible direction, as a ground of arrangement. We shall consider the possible or probable forms or contours of arches in the present Chapter, and in the succeeding one the forms of voussoir and other help which may best fortify these visible lines against every temptation to lose their consistency.

Fig. XXX.

§ X. Look back to [Fig. XXIX.] Evidently the abstract or ghost line of the arrangement at A is a plain horizontal line, as here at a, [Fig. XXX.] The abstract line of the arrangement at B, [Fig. XXIX.], is composed of two straight lines, set against each other, as here at b. The abstract line of C, [Fig. XXIX.], is a curve of some kind, not at present determined, suppose c, [Fig. XXX.] Then, as b is two of the straight lines at a, set up against each other, we may conceive an arrangement, d, made up of two of the curved lines at c, set against each other. This is called a pointed arch, which is a contradiction in terms: it ought to be called a curved gable; but it must keep the name it has got.

Now a, b, c, d, [Fig. XXX.], are the ghosts of the lintel, the gable, the arch, and the pointed arch. With the poor lintel ghost we need trouble ourselves no farther; there are no changes in him: but there is much variety in the other three, and the method of their variety will be best discerned by studying b and d, as subordinate to and connected with the simple arch at c.

§ XI. Many architects, especially the worst, have been very curious in designing out of the way arches,—elliptical arches, and four-centred arches, so called, and other singularities. The good architects have generally been content, and we for the present will be so, with God’s arch, the arch of the rainbow and of the apparent heaven, and which the sun shapes for us as it sets and rises. Let us watch the sun for a moment as it climbs: when it is a quarter up, it will give us the arch a, [Fig. XXXI.]; when it is half up, b, and when three quarters up, c. There will be an infinite number of arches between these, but we will take these as sufficient representatives of all. Then a is the low arch, b the central or pure arch, c the high arch, and the rays of the sun would have drawn for us their voussoirs.

§ XII. We will take these several arches successively, and fixing the top of each accurately, draw two right lines thence to its base, d, e, f, [Fig. XXXI.] Then these lines give us the relative gables of each of the arches; d is the Italian or southern gable, e the central gable, f the Gothic gable.

Fig. XXXI.