147. From these principles of simplicity and temperance, two very severely fixed laws of construction follow; namely, first, that our structure, to be beautiful, must be produced with tools of men; and, secondly, that it must be composed of natural substances. First, I say, produced with tools of men. All fine art requires the application of the whole strength and subtlety of the body, so that such art is not possible to any sickly person, but involves the action and force of a strong man's arm from the shoulder, as well as the delicatest touch of his fingers: and it is the evidence that this full and fine strength has been spent on it which makes the art executively noble; so that no instrument must be used, habitually, which is either too heavy to be delicately restrained, or too small and weak to transmit a vigorous impulse; much less any mechanical aid, such as would render the sensibility of the fingers ineffectual.[29] 148. Of course, any kind of work in glass, or in metal, on a large scale, involves some painful endurance of heat; and working in clay, some habitual endurance of cold; but the point beyond which the effort must not be carried is marked by loss of power of manipulation. As long as the eyes and fingers have complete command of the material, (as a glass-blower has, for instance, in doing fine ornamental work,)--the law is not violated; but all our great engine and furnace work, in gun-making and the like, is degrading to the intellect; and no nation can long persist in it without losing many of its human faculties. Nay, even the use of machinery other than the common rope and pulley, for the lifting of weights, is degrading to architecture; the invention of expedients for the raising of enormous stones has always been a characteristic of partly savage or corrupted races. A block of marble not larger than a cart with a couple of oxen could carry, and a cross-beam, with a couple of pulleys, raise, is as large as should generally be used in any building. The employment of large masses is sure to lead to vulgar exhibitions of geometrical arrangement,[30] and to draw away the attention from the sculpture. In general, rocks naturally break into such pieces as the human beings that have to build with them can easily lift; and no larger should be sought for. 149. In this respect, and in many other subtle ways, the law that the work is to be with tools of men is connected with the farther condition of its modesty, that it is to be wrought in substance provided by Nature, and to have a faithful respect to all the essential qualities of such substance.