Chapter I

shall consider the second, under the head, Arch Masonry.

§ 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.

[Illustration: 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.

[Illustration: Fig. XXXI.]

§ XIII. We will again take the three arches with their gables in succession, and on each of the sides of the gable, between it and the arch, we will describe another arch, as at _g_, _h_, _i_. Then the curves so described give the pointed arches belonging to each of the round arches; _g_, the flat pointed arch, _h_, the central pointed arch, and _i_, the lancet pointed arch.

§ XIV. If the radius with which these intermediate curves are drawn be the base of _f_, the last is the equilateral pointed arch, one of great importance in Gothic work. But between the gable and circle, in all the three figures, there are an infinite number of pointed arches, describable with different radii; and the three round arches, be it remembered, are themselves representatives of an infinite number, passing from the flattest conceivable curve, through the semicircle and horseshoe, up to the full circle.

The central and the last group are the most important. The central round, or semicircle, is the Roman, the Byzantine, and Norman arch; and its relative pointed includes one wide branch of Gothic. The horseshoe round is the Arabic and Moorish arch, and its relative pointed includes the whole range of Arabic and lancet, or Early English and French Gothics. I mean of course by the relative pointed, the entire group of which the equilateral arch is the representative. Between it and the outer horseshoe, as this latter rises higher, the reader will find, on experiment, the great families of what may be called the horseshoe pointed,--curves of the highest importance, but which are all included, with English lancet, under the term, relative pointed of the horseshoe arch.

[Illustration: Fig. XXXII.]

§ XV. The groups above described are all formed of circular arcs, and include all truly useful and beautiful arches for ordinary work. I believe that singular and complicated curves are made use of in modern engineering, but with these the general reader can have no concern: the Ponte della Trinita at Florence is the most graceful instance I know of such structure; the arch made use of being very subtle, and approximating to the low ellipse; for which, in common work, a barbarous pointed arch, called four-centred, and composed of bits of circles, is substituted by the English builders. The high ellipse, I believe, exists in eastern architecture. I have never myself met with it on a large scale; but it occurs in the niches of the later portions of the Ducal palace at Venice, together with a singular hyperbolic arch, _a_ in Fig. XXXIII., to be described hereafter: with such caprices we are not here concerned.

§ XVI. We are, however, concerned to notice the absurdity of another form of arch, which, with the four-centred, belongs to the English perpendicular Gothic.

Taking the gable of any of the groups in Fig. XXXI. (suppose the equilateral), here at _b_, in Fig. XXXIII., the dotted line representing the relative pointed arch, we may evidently conceive an arch formed by reversed curves on the inside of the gable, as here shown by the inner curved lines. I imagine the reader by this time knows enough of the nature of arches to understand that, whatever strength or stability was gained by the curve on the _outside_ of the gable, exactly so much is lost by curves on the _inside_. The natural tendency of such an arch to dissolution by its own mere weight renders it a feature of detestable ugliness, wherever it occurs on a large scale. It is eminently characteristic of Tudor work, and it is the profile of the Chinese roof (I say on a large scale, because this as well as all other capricious arches, may be made secure by their masonry when small, but not otherwise). Some allowable modifications of it will be noticed in the chapter on Roofs.

[Illustration: Fig. XXXIII.]

§ XVII. There is only one more form of arch which we have to notice. When the last described arch is used, not as the principal arrangement, but as a mere heading to a common pointed arch, we have the form _c_, Fig. XXXIII. Now this is better than the entirely reversed arch for two reasons; first, less of the line is weakened by reversing; secondly, the double curve has a very high æsthetic value, not existing in the mere segments of circles. For these reasons arches of this kind are not only admissible, but even of great desirableness, when their scale and masonry render them secure, but above a certain scale they are altogether barbarous; and, with the reversed Tudor arch, wantonly employed, are the characteristics of the worst and meanest schools of architecture, past or present.

This double curve is called the Ogee; it is the profile of many German leaden roofs, of many Turkish domes (there more excusable, because associated and in sympathy with exquisitely managed arches of the same line in the walls below), of Tudor turrets, as in Henry the Seventh's Chapel, and it is at the bottom or top of sundry other blunders all over the world.

§ XVIII. The varieties of the ogee curve are infinite, as the reversed portion of it may be engrafted on every other form of arch, horseshoe, round, or pointed. Whatever is generally worthy of note in these varieties, and in other arches of caprice, we shall best discover by examining their masonry; for it is by their good masonry only that they are rendered either stable or beautiful. To this question, then, let us address ourselves.

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