These great effects of light and shade, obtained by the plan--effects simple in their means, yet mysterious in their power of attraction for us, have strengthened the idea that Gothic art is idealistic. The masses who see the cathedral dominating the city, with its two slanting roofs like hands joined at the finger-tips, certainly feel in it the great idea, the poem. They do not realize that the sentiments aroused in them by the beauty of the building are wholly due to the science of the plans. By means of what principle did the master builders support the weight of these enormous masses of stone, which yet join lovingly in the imponderable atmosphere? By obeying the law of equilibrium of the human body. The human body, standing upright, the feet joined, in equilibrium, is the basis of the Greek column. Pediments and roof, supported by a series of these standing bodies, these human columns, that is the Greek temple. The architecture of the Parthenon reproduces the equilibrium of the body in a state of rest. In action the body sways; that is to say, the weight rests on only one leg, while the body inclines to the opposite side to regain its balance by counterpoise. That is the sway of Gothic architecture. This sway constitutes the law of motion for the body of man and animal, ever seeking perfect equilibrium. Without this law we could not move; we would be like blocks of stone. Every motion that we make produces an initial swaying, which an opposing weight instantaneously balances. Thus without any consciousness on our part a perpetual balancing is taking place within us, a change as facile and immediate as the changes which take place in the phenomena of respiration and circulation. All goes on with the speed, order, and silence that exist in the domain of electricity. It is a perpetual prodigy to which we do not even give a thought. It is not surprising that the Gothic masters, who copied from all nature, took from man and animals the charm of balance. The ogive (pointed arch) of the cathedral, is achieved by two opposing thrusts. But the archivolts do not always harmonize with the capitals; they are not set exactly over them, they are out of the perpendicular. Two movements of equal force, exactly opposed, cause a stable equilibrium. Just so the masses of stone are supported by this same opposition of thrusts. The interior of the cathedral is high and vast, broken by large windows that diminish the resistance and help to support the great weight. It was necessary to find a way of reëstablishing the equilibrium, lest the nave break down under its own weight. That is the purpose of the flying buttresses. Like the arms of giants, they throw their opposing weight against the exterior walls. Some have drawn the conclusion that cathedrals are imperfect, since they cannot stand without this support. It is a characteristic idea of our age. Just as though one would reproach the human body for bearing first on one leg and then on the other.