Galilei, Galileo, Discourse concerning the natation of bodies, 1663

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              and future, eſpecially if the time be for many Moneths or Years; I
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              am therefore forced, with other Obſervations, and more exact than
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              the former, and in times more remote from one another, to correct
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              the Tables of ſuch Motions, and limit them even to the ſhorteſt mo­
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              ment: for ſuch exactneſſe my firſt Obſervations ſuffice not; not only
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              in regard of the ſhort intervals of Time, but becauſe I had not as then
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              found out a way to meaſure the diſtances between the ſaid Planets
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              by any Inſtrument: I Obſerved ſuch Intervals with ſimple relation
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              to the Diameter of the Body of
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              Jupiter
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              ; taken, as we have ſaid, by
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              the eye, the which, though they admit not errors of above a Minute,
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              yet they ſuffice not for the determination of the exact greatneſs of the
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              Spheres of thoſe Stars. </s>
              <s>But now that I have hit upon a way of ta­
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              king ſuch meaſures without failing, ſcarce in a very few Seconds, I will
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              continue the obſervation to the very occultation of
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              JVPITER,
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              which ſhall ſerve to bring us to the perfect knowledge of the Moti­
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              ons, and Magnitudes of the Orbes of the ſaid Planets, together
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              alſo with ſome other conſequences thence ariſing. </s>
              <s>I adde to theſe
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              things the obſervation of ſome obſcure Spots, which are diſcover­
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              ed in the Solar Body, which changing, poſition in that, propounds
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              to our conſideration a great argument either that the Sun revolves in
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              it ſelfe, or that perhaps other Starts, in like manner as
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              Venus
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              and
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              Mercury,
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              revolve about it, inviſible in other times, by reaſon of their
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              ſmall digreſſions, leſſe than that of
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              Mercury,
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              and only viſible when
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              they interpoſe between the Sun and our eye, or elſe hint the truth
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              of both this and that; the certainty of which things ought not to be
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              contemned, nor omitted.</s>
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              The Authors
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              Obſervations of
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              the Solar Spots.</s>
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              <s>
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              Continuall obſervation hath at laſt aſſured me that theſe Spots are
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              matters contiguous to the Body of the Sun, there continually produced
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              in great number, and afterwards diſſolved, ſome in a ſhorter, ſome in a
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              longer time, and to be by the Converſion or Revolution of the Sun in it
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              ſelfe, which in a Lunar Moneth, or thereabouts, finiſheth its Period,
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              caried about in a Circle, an accident great of it ſelfe, and greater for
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              its Conſequences.
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              </s>
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              The occaſion in­
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              ducing the Au­
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              thor to write
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              this Treatiſe.</s>
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              <s>As to the other particular in the next place. ^{*} Many cauſes have
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              moved me to write the preſent Tract, the ſubject whereof, is the
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              Diſpute which I held ſome dayes ſince, with ſome learned men of
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              this City, about which, as your Highneſſe knows, have followed
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              many Diſcourſes: The principall of which Cauſes hath been the
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              Intimation of your Highneſſe, having commended to me Writing,
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              as a ſingular means to make true known from falſe, reall from appa­
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              rent Reaſons, farr better than by Diſputing vocally, where the
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              one or the other, or very often both the Diſputants, through too </s>
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          </chap>
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