Either a weight is hung from the axle of the principal wheel, and by its tension causes the axle, the wheel to which it belongs, and the other wheels to turn; or a long strip of steel is forcibly bound round the axle, and by its endeavours to get free and straighten itself, makes the axle and the wheel turn round. In order that the rotation may not be too fast, but slow like that of the vault of heaven, other wheels are added, of which the last, driven by two teeth only, makes a clicking noise and is analogous to the change between the coming and the going light, or to that between day and night. In addition to that part of the mechanism which gives the signal for the hours and the quarters, skilfully-devised triggers are added, which set it in motion at the right time, and then stop it again, just as nature, by the movement of the vault of heaven, allows winter, spring, summer, and autumn to come and to depart again at the right moment.
7. It is now quite clear that that order, which is the dominating principle in the art of teaching all things to all men, should be, and can be, borrowed from no other source but the operations of nature. As soon as this principle is thoroughly secured, the processes of art will proceed as easily and as spontaneously as those of nature. Very aptly does Cicero say: “If we take nature as our guide, she will never lead us astray,” and also: “Under the guidance of nature it is impossible to go astray.” This is our belief, and our advice is to watch the operations of nature carefully and to imitate them.
8. But some one may laugh at our expectations and may cast in our teeth the saying of Hippocrates: “Life is short, and art is long; opportunities are fleeting, experience is deceptive, and judgment is difficult.” Here are five obstacles, the reasons why so few scale the heights of wisdom:—
(i) The shortness of life; through which so many are snatched away in youth before their preparations for life are finished. (ii) The perplexing crowd of objects which
