itself by numerous experiments; as particularly in bubbles; the sphericity of drops; the fine threads of isicles; in the drawing out of glutinous bodies, &c. But this appetite principally appears, when a discontinuation is attempted in the small parts of bodies: thus, in beating the mortar, after the pulverization is carried to a certain degree, the pestle operates no further upon the matter to reduce it finer. And so water will not enter into fine cracks, or fissures; nor air, though so extremely subtile, readily insinuate into the pores of solid vessels.

Let the sixth motion be that we call motion of acquisition, or motion of want; by which bodies, when placed among others that are heterogeneous to, and, as it were at enmity with them, if they find an opportunity of flying and avoiding these, and applying themselves to others nearer related, though without any close or intimate consent, yet they presently embrace the occasion, and chuse the latter before the former, as it were, in the way of acquisition, or as if they stood in want of such bodies, from whence we derive the name.

For example, leaf-gold, or any other metal in the leaf, delights not in the ambient air; and therefore if it touches any tangible or gross body, as the finger, paper, &c. it presently sticks thereto, and is hot easily separated again.

So paper, cloth, &c. have no great agreement with the air residing or lodged in the pores thereof, and therefore such bodies readily imbibe water or other moisture, and reject or throw out the air. So if sugar or sponge be dipt only at one end in water or wine, whilst the other part remains far above the surface of the liquor; yet these bodies gradually attract the wine and water upwards *.

Hence we may derive an excellent rule for the opening and dissolving of bodies; for, (not to meddle at present with corrosive menstruums, which force themselves a passage) if a suitable body can be found that has a greater agreement. or consent with any solid, than the matter has wherewith such a solid is mixed, as it were by necessity +; the solid will immediately open and relax itself, to receive the latter and exclude and reject the formert. Nor does this motion of acquisition operate only in immediate contact,

* See the Sylva Sylvarum, under the article Attraction. + The Instances hereof are numerous in chemistry, as in adding oil of vitriol to nitre, sea-salt, &c. when the oil of vitriol seizes upon the earthy part, and sets the spirit of nitre, &c. free.

See the article Attraction in the Sylva Sylvarum. See also the chapter of Menstruum in Boerhaave's Chemistry; and M. Geoffroy's Table of the different relations observed in Chemistry, betwixt different bodies, in the French Memoirs. Ann. 1718.

for the electrical virtue (about which Dr. Gilbert and others have invented such fables) is an appetite excited by a gentle friction, and not well. agreeing with, or enduring the air, but affects or covets other tangible bodies, if it finds them near at hand *.

Let the seventh motion be that we call the motion of the greater congregation, whereby bodies are carried to the masses of their own natures; heavy ones to the globe of the earth, and light ones to surrounding heavens. This, by the schools, from a superficial consideration, is called natural motion; because they found nothing that was externally visible to give it, and therefore imagined it to reside naturally, or to be innate in things themselves: or again, perhaps because it is a ceaseless or continual motion. And no wonder, since the heavens and the earth are always at hand; whereas the causes and origins of many other motions are sometimes present and sometimes absent; and hence they laid this down for a constant and proper motion, and the others for acquired ones.

But, in reality, this motion is weak and languid, as yielding and submitting to other motions, so long as they continue to operate, un

*See Mr. Boyle of Electricity. See also the Author's Sylva Sylvarum, under the article Electricity.

less the b bulk of the body be considerable. Ande although this motion has so possessed the thoughts

of men as almost to have stifled or superseded the rest; yet it is very little that they know thereof, but run into many errors about it *.

Let the eighth motion be the motion of the lesser congregation, whereby the homogeneous parts in any one body separate themselves from the heterogeneous, or collect together, and where by also distinct and entire bodies, from a simili-1, tude of substance, embrace, cherish, and some times collect and attract each other, and come together from a certain distance, as when in milk, the cream after some continuance floats a-top; and in wine, the lees sink to the bottom. Nor does it happen only through the motion of gravity and levity, that some parts should rise to the top, and others sink to the bottom; but much more through an appetite, that homoge neous bodies have of meeting and uniting toge ther.

This motion differs from the motion of want in two respects; the one, that in the motion of want there is a stimulus, or incitement of a malignant and contrary nature, whereas in this motion, when all obstacles and impediments are removed, the parts unite by congruity or affec

* See the article Motion in the Sylva Sylvarum

解

tion, though there be no foreign nature present to cause an aversion. The other respect is, that the union here proves closer, and, as it were, stronger, with greater appetite or choice. For, in the former, if the thing at enmity be avoided, the bodies meet, though they are not greatly related; but in the latter, substances come together, as if perfectly related by similitude, and make, as it were, one whole. And this motion resides in all compound bodies, and would easily shew itself in each, if it were not bound down and restrained by other appetites, and necessities of bodies, which disturb and hinder this union*.

This motion is generally bound down three ways, viz. 1. by the inactivity of bodies; 2. by the check of a predominating body; and, 3. by external motion. As to the first, it is certain that tangible bodies have a kind of inactivity or sluggishness, in a greater or less degree, whereby they dread or resist local motion, so that, unless excited, they tend rather to continue in their present state, than to move or change for a better +.

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*These appetites, or laws of motion, require the strictest regard, as being the things whereon all the actions and passions, or all the phænomena and effects of bodies, principally depend.

+ This seems to be what is now called, by mathematical writers, the vis inertia of matter..