The Motion of Excitement

16. The motion of royal or political motion

This makes the predominant and governing parts of any body:

• check, subdue, reduce, and regulate the others
• force them to unite, separate, stand still, move, or assume a certain position, not from any inclination of their own, but according to a certain order, and as best suits the convenience of the governing part.

In this way, there is a sort of dominion and civil government exercised by the ruling part over its subjects.

The motion is very conspicuous in the spirits of animals, where, as long as it is in force, it tempers all the motions of the other parts.

It is found in a less degree in other bodies, as we have observed in blood and urine, which are not decomposed until the spirit, which mixed and retained their parts, has been emitted or extinguished.

Nor is this motion peculiar to spirits only, although in most bodies the spirit predominates, owing to its rapid motion and penetration; for the grosser parts predominate in denser bodies, which are not filled with a quick and active spirit (such as exists in quicksilver or vitriol), so that unless this check or yoke be thrown off by some contrivance, there is no hope of any transformation of such bodies.

And let not any one suppose that we have forgotten our subject, because we speak of predominance in this classification of motions, which is made entirely with the view of assisting the investigation of wrestling instances, or instances of predominance.

I do not now treat of the general predominance of motions or powers, but of that of parts in whole bodies, which constitutes the particular species here considered.

17. Spontaneous motion[264] of Revolution

This makes bodies which have a tendency to move, and placed in a favorable situation, enjoy their peculiar nature. They pursue themselves and nothing else, seeking to embrace themselves.

For bodies seem either to move without any limit, or to tend toward a limit, arrived at which they either revolve according to their peculiar nature, or rest.

Those which are favorably situated, and have a tendency to motion, move in a circle with an eternal and unlimited motion.

Those which are favorably situated and abhor motion, rest. Those which are not favorably situated move in a straight line (as their shortest path), in order to unite with others of a congenial nature.

This motion of revolution has 9 differences:

1. with regard to the centre about which the bodies move
2. the poles round which they move
3. the circumference or orbit relatively to its distance from the centre
4. the velocity, or greater or less speed with which they revolve
5. the direction of the motion as from east to west, or the reverse
6. the deviation from a perfect circle, by spiral lines at a greater or less distance from the centre
7. the deviation from the circle, by spiral lines at a greater or less distance from the poles
8. the greater or less distance of these spirals from each other
9. the variation of the poles if they be movable; which, however, only affects revolution when circular.

The motion in question is, according to common and long-received opinion, considered to be that of the heavenly bodies. There exists, however, with regard to this, a considerable dispute between some of the ancients as well as moderns, who have attributed a motion of revolution to the earth.

A much more reasonable controversy, perhaps, exists (if it be not a matter beyond dispute), whether the motion in question (on[265] the hypothesis of the earth’s being fixed) is confined to the heavens, or rather descends and is communicated to the air and water. The rotation of missiles, as in darts, musket-balls, and the like, we refer entirely to the motion of liberty.

18. The motion of trepidation

[160] to which (in the sense assigned to it by astronomers) we do not give much credit; but in our serious and general search after the tendencies of natural bodies, this motion occurs, and appears worthy of forming a distinct species.

It is the motion of an (as it were) eternal captivity; when bodies, for instance, being placed not altogether according to their nature, and yet not exactly ill, constantly tremble, and are restless, not contented with their position, and yet not daring to advance.

Such is the motion of the heart and pulse of animals, and it must necessarily occur in all bodies which are situated in a mean state, between conveniences and inconveniences; so that being removed from their proper position, they strive to escape, are repulsed, and again continue to make the attempt.