CAP. III. DE GRAD. VIRT. MOTIV. VITAL. &c.

This common opinion seems to have such verisimilitude and probability in itself that it is not a wonder that it has been revoked into doubt by no one, so far as I know. For who would be so foolish as to ever seek a machine to move a small weight with great force, that is, to employ a machine and artifice not as a shortcut, but to suffer a waste of strength? It is no different than if someone, to move and lift a weight of one pound—which they could move immediately without any machine with a force and strength equal to one pound—should neglect the shortcut and seek levers, pulleys, and other organs to lift that one pound with forces ten or a hundred times greater. And if this is justly considered absurd, how can it happen that the most wise Nature, who everywhere seeks shortcuts, simplicity, and ease, has worked with such industry to construct machines in the organs of an animal, not to move great weights with small virtue, but on the contrary, to move small weights with an almost immense strength?

Although this may seem a monster and contrary to the common opinion, I do not deny that I can demonstrate it most evidently and, having first asked permission, show that the assertors of the contrary opinion have been deceived. For I shall demonstrate that machines are truly used in the motions of an animal, and that they are manifold and various; yet, that great weights are not lifted with small virtue, but on the contrary, small weights are sustained by a great virtue and strength of the animal faculty, so that the motive virtue many times exceeds the weight of the bones and lifted joints a hundred and a thousand times, and is never less than them; and this will be the principal subject and matter of this first part.

CAPUT IV.

Theoremata utilia ad ostendendam immensitatem virtutis motivæ Musculorum. Useful theorems for demonstrating the immensity of the motive virtue of the muscles.

PROPOSITIO IX.

Motus Articulorum flexivus sphæricus est, vel circularis, aut in superficie conica circa centrum imaginarium factus. The flexing motion of the joints is spherical, or circular, or made on a conical surface around an imaginary center.

In all flexions of the joints, it must first be seen how the bones are moved and what figure they constitute in their motions.

And first, there is no doubt that almost all motions of the parts of an animal are circular, or composed of circular ones. This, however, is sufficiently...