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of Waters; An Instrument to examine the greatest Depths of the Seas; Another, to try for fresh waters in the bottoms of some Seas; Pendulum-watches to ascertain Longitudes. But I must refer to a greater store of such useful Inventions commemorated by Mr Sprat in his History of the R. Society.
Neither had I here mention'd these, but to give this Advertisement; That sometimes one of these Instruments may open a fair Portal for more Volumes of the most obliging Philosophy, than can he absolv'd by many hands in some Ages. It will not be meer Preface, but closely agreeable to the Intention of these Tracts, if I here instance one particular, which may possibly seem to some of the lowest value, and yet may chance to prove of greater importance, than at first we are apt to imagine. I will name good Scales both of the nicest kinds, and some of a stronger frame. Now this I would represent. 'Tis certain, some Bodies do increase their weight in a strong Fire: See the Experiment in the said Hist. of the R. Society, p, 228. And Honorable Mr Boyle hath proved, That even Solid and Coldest Bodies have their Atmospheres; Some their Electricity; and same their Magnetismes: And 'tis palpahle, that some draw more Aliment, either from the Earth, or from subterraneous Liquors, or Spirits, or from the Nutritious parts of the Air, or other Influences, which descend through the Air, than they expend in their Atmospheres; And perhaps more at certain State times, till they have acquired their due Increment. This being observ'd, it seems easie to devise, How to examine by Scales, Glasses, and such slight furniture, whence Vegetables, many kinds of Stones, Metals, and other Minerals, have more or less of their Increment, and whence they obtain the stronger Fermentation, which conserves them, or promotes their perfection in their kind: Whether Glass, or what other Materials, do obstruct or retard the resort of any or all of these Spirits, Heats, or Influences: Whether Evergreens, the most fragrant or strong-senting, hot or cold Plants, draw more of their substance from the free Air; and which draw more from the subterraneal supplyes, And so we may examine Earths; and Minerals. We see many Tracts of Land, which yield peculiar Ferments, sometimes Vitriolate Earth, sometimes Aluminous, sometimes Nitrous, sometimes common-Saline, healing Bolus's, and Earth proper for Fullers, Tobacco-pipes, &c. Sometimes the ferment is so hot, as to hollow the surface faster than can easily be
