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SECT. II.
COncerning the immediate Causes of Rarity and Density in Bodies,* 1.1 di∣vers Conceptions are delivered by Philosophers. (1) Some, ob∣serving that Rare bodies generally are less, and Dense more Ponderous, and that the Division of a body into small parts, doth usually make it less swift in its descent through aer or water, than while it was intire; have thereupon determined the Reason of Rarity to consist in the actual division of a body into many small parts: and, on the contrary, that of Density to consist in the Coadunation or Compaction of many small parts in∣to one great continued mass. But, These considered not, that Chrystal is not more rare, though less weighty (proportionately) than a Dia∣mond: nor that the Velocity of bodies descending, doth not encrease in proportion to the difference of their several Densities, as their inad∣vertency made them praesume; there being sundry other Causes, besides the Density of a body, assignable to its greater Velocity of motion in descent, as the Heroical pen of Galileo hath clearly demonstrated (in 1. Dialog. de motu.) and our selves shall professedly evince in convenient place.
(2) Others,* 1.2 indecently leaping from Physical to Metaphysical specu∣lations, and imagining the substance of a body to be a thing really di∣st••nct from the Quantity thereof; have derived Rarity and Density from the ••••veral proportions, which Quantity hath to its substance; as if in Ra∣refaction a Body did receive no mutation of Figure, but an Augmentation, and in Condensation a Diminution of its Quantity. But the excessive subtility, or rather absolute incomprehensibility of this Distinction, doth evidently confess it to be meerly Chimerical, as we have formerly inti∣mated, in our discourse concerning the proper and genuine notions of Corporiety and Inanity.
(3) A Third sort there are,* 1.3 who having detected the incompetency of the first opinion, and absolute unintelligibility of the Second; judiciously desume the more or less of Rarity in any body, from the more or less of Vacuity intercepted among the parts thereof; and on the contrary, the more or less of Density from the greater or less exclusion of Inanity, by the reduction of the parts of a body to mutual Contingency. And this is that opinion, which only hath subjugated our judgement, and which seems worthy our best patronage: in regard not only of its sufficiency to expli∣cate all the various Apparences among bodies, resulting from their seve∣ral Differences in Rarity and Density; but also of its exuperance of rea∣son above the F••rst, and of intelligibility above the second; it being the duety of a Philosopher, always to prefer Perspicuity to Obscurity, plain and genuine notions to such as are abstracted not farther from mat∣ter, than all possibility of Comprehension.