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Before I enter upon new matter, I shall beg the Readers leave to cast an Eye back, as formerly, and review what we have endeavour'd to do hitherto, that I may remark the concernments, why, and upon what occasion I adopted the Arguments all along; and that I may thence take fresh encouragement, and clearer instruction for our future Collections.
In the last Preface before our fourth Volum, I gave a Synopsis of the main importance of our three foregoing Books, inserting a particular recommendation of the extensive Usefulness of such Artificial Instruments lately invented. To the Catalogue of Instruments there recited, or hinted, we have since added (in the 4th Vol.) some Inventions or Applications, which either have not been formerly thought of; or have been long sought and in vain attempted, or have made discovery's contrary to old Expectations, and even sometimes to the confident Affections of Acute and very Inquisitive men. What Peripatetick would endure to hear of weighing water in water? There we have a Demonstration, How to estimate the particular weight of any quantity of Liquors in Liquors, exactly, and by ordinary Balances and Weights. And this is performed by the same happy hand; which before directed us, How to find and denominate the particular Weight of any parcel if Air in Air, or of any Pillar of Air of the whole Atmo-sphere, of any size, in any place where we can come, whether clear'd, or laden with exhalations, clouds, snow, hail, or other Meteors, horn high soever they ascend; and the same slight Engin (the Ballance) hath in the same hand detected an Atmosphere in the most Solid Bodies.
'Tis a longtime since the Mechanical Witts have consulted, How to improve Optical Glasses by the Hyperbolical Section: There we have the Proposition demonstrated, and the Engin directed for practice. The skill of drawing in Perspective is as a pleasant Companion to the Travaylor, and enables him to given a lively History of his Travels for the information of others: There we may find, how to draw in Perspective, any Objects both accurately and dispatchingly, by an Instrument; as any vulgar hand may draw a Circle more perfectly by a Compass, than the most perfect Penman can do by his hand alone: And we have gotten a little step on toward the advancing of Metalline Burning Concaves, of which the performance is there particularised.
We
