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from assimilation; as when clay, mixed among stones, concretes, and is turned into a stony matter; or when the scales of the teeth are turned into a substance as hard as the teeth themselves, &c. For we judge that all bodies have an appetite of assimilating, as well as of uniting what is homogeneous to themselves, but that both powers are bound down or suppressed, though not in the same manner. All these ways of binding, and the correspondent ones of loosing, should be diligently enquired after, because they regard the prolongation of Life, or the alleviation of old age*.

Lastly, it is worth observing, that in the ten preceding motions bodies seem only to affect or endeavour the preservation of their own natures; but in this eleventh, to endeavour their propagation.

Let the twelfth motion be the motion of excitation; which seems of the same kind with the motion of assimilation, as being diffusive, communicative, transitive, and multiplicative, like that, so as generally to agree therewith in the effect, though they differ in the subject and manner of effecting; for the motion of assimilation proceeds with a kind of sway, authority, and power, as it commands and compels the matter assimilated to turn and change into the matter

* See the author's History of Life and Death.

assimilating; whereas the motion of excitation proceeds as if it were by art, insinuation, and stealth; thus soliciting and disposing the excited matter to assume the nature of the matter exciting. So, again, the motion of assimilation multiplies and transforms bodies and substances, and thus produces more flame, more air, more spirit, more flesh, &c. but in the motion of excitation none but virtues are multiplied and communicated; whence there is generated more heat, more magnetism, more putrefaction, &c.

And this motion is remarkably found in heat and cold; for heat does not diffuse itself in heating, by the communication of the original heat, but only by exciting the parts of the body to that motion which is the form of heat, as was mentioned above*, and therefore heat is much slower and more difficultly excited in stone or metal than in air, by reason of the indisposition and unfitness of those bodies to admit of that motion; whence, possibly, there may lodge in the bowels of the earth matters which cannot be heated, as being, by a greater condensation, deprived of that spirit with which this motion of excitation generally begins †.

See Aph. 13. and 20.

t Consult the tables above laid down, Aph, 11, 12, 13, 18, 20.

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So the magnet gives iron a new disposition of parts and a conformable motion, whilst itself loses nothing of its virtue. So likewise bakers leaven, yeast, rennet, and certain poisons, respectively excite and solicit a successive and continued motion, in the coming of cheese, the making of bread, the fermenting of beer, and in poisoning the human body; and this not so much by the power of the exciting matters, as by the predisposition and easy yielding of the bodies excited.

Let the thirteenth motion, be the motion of impression, which likewise seems of the same kind with the motion of assimilation, and is the most subtile of diffusive motions; but we think proper to make it a species by itself, because of a remarkable difference it has in respect of the two former. For the simple motion of assimilation transforms bodies themselves, so that if what gave the first motion be removed, it is of no significance to what follows; for the first lighting up of flame, or the first conversion into air, makes nothing to the succeeding generation of flame or air. So likewise motion of excitation remains perfect for a considerable time after the first mover is taken away, as in a heated body, after what gave the first heat is removed; in animated iron, after the loadstone is laid aside; and in bread before baking, when the leaven is taken away. But the motion of impression,

though it be diffusive and transitive, yet seems constantly to depend upon the first mover, so as if that be taken away, it immediately ceases, and comes to nothing. This motion is, therefore, performed momentaneously, or at least suddenly, for which reason we call the motions of assimilation and excitation the motions of Jupiter's generation, because the generation remains; but this motion of impression, the motion of Saturn's generation, because the offspring is presently devoured and swallowed up.

This motion shews itself in three things, viz 1. the rays of light; 2. the percussion of sounds; and, 3. the communication of magnetical virtues. For, 1. when light is removed, colour and all visible appearances immediately vanish; and, 2. upon removal of the first percussion, and the concussion of the body consequent thereto, sound soon vanishes. For although sounds are tossed and agitated in their medium by winds, as it were by waves, yet it must be carefully observed, that sound does not continue so long as the resounding continues. For when a bell is struck, the sound seems to continue a good while after, but it would be very erroneous hence to conceive, that the sound fluctuated, and hung in the air, all that while; for the resounding is not the same numerical sound, but a new one, as appears plainly by stopping the body struck, so if the

bell be strongly compressed whilst it resounds, and be thus rendered motionless, the sound instantly ceases, and no more resounding is heard. So likewise in stringed instruments, if the string: be touched with the finger, after the first percussion, the resounding presently stops. 3. And, lastly, when the magnet is removed, the iron suspended by it presently falls down; but the moon cannot by us be removed from the sea, nor the earth from a ponderous body in falling; and, therefore, no experiment can, in this respect, be made on them, though the case be otherwise the same *.

Let the fourteenth motion be the motion of configuration, or situation, whereby bodies seem not to affect coming to, or flying from one ano¬ ther, but a certain position, situation, and configuration, with respect to others. This, indeed, is a very abstruse motion, and little enquired into; and, in some cases, it seems to be without a cause, though we judge it not to be really so.

Thus, if it should be asked why the heavens revolve from east to west, than from west to

* Sir Isaac Newton attempts to shew, by calculation, that the moon, and whole solar system, may be sensibly affected by the attraction of the earth, and conjectures that the effect will become more sensible hereafter, by causing a great disturbance in the celestial motions. Sce Newton. Princip. Lib. III.

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