Galilei, Galileo
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The systems of the world
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1661
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go accompanied with thoſe illuminating beams of the Sun.</
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<
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>SIMPL. </
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<
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>This is true, without any contradiction.</
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>SALV. </
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>But when the Moon is oppoſite to the Sun, what
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ference is there between the tract of the rayes of your ſight, and
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that motion which the Suns rayes make?</
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>SIMPL. </
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<
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>Now I underſtand you; for you would ſay, that the
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rayes of the ſight and thoſe of the Sun, moving by the ſame lines,
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we cannot perceive any of the obſcure valleys of the Moon. </
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>Be
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pleaſed to change this your opinion, that I have either ſimulation
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or diſſimulation in me; for I proteſt unto you, as I am a
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man, that I did not gueſſe at this ſolution, nor ſhould I have
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thought upon it, without your help, or without long ſtudy.</
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<
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>SAGR. </
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>The reſolutions, which between you two have been
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alledged touching this laſt doubt, hath, to ſpeak the truth,
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ed me alſo. </
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>But at the ſame time this conſideration of the
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fible rayes accompanying the rayes of the Sun, hath begotten in me
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another ſcruple, about the other part, but I know not whether I
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can expreſſe it right, or no: for it but juſt now comming into my
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mind, I have not yet methodized it to my mind: but let us ſee if
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we can, all together, make it intelligible. </
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>There is no queſtion,
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but that the parts towards the circumference of that poliſh't, but not
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burniſh't Hemiſphere, which is illuminated by the Sun, receiving the
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rayes obliquely, receive much fewer thereof, than the
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moſt parts, which receive them directly. </
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<
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>And its poſſible, that a
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tract or ſpace of
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v. </
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<
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twenty degrees in breadth, and which is
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wards the extremity of the Hemiſphere, may not receive more rays
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than another towards the middle parts, of but four degree broad:
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ſo that that doubtleſs will be much more obſcure than this; and
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ſuch it will appear to whoever ſhall behold them both in the face,
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or (as I may ſay) in their full magnitude. </
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>But if the eye of the
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beholder were conſtituted in ſuch a place, that the breadth of the
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twenty degrees of the obſcure ſpace, appeared not to it longer
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than one of four degrees, placed in the midſt of the Hemiſphere,
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I hold it not impoſſible for it to appear to the ſaid beholder
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qually clear and lucid with the other; becauſe, finally, between
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two equal angles, to wit, of four degrees apiece, there come to
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the eye the reflections of two equal numbers of rayes: namely,
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thoſe which are reflected from the middlemoſt ſpace, four degrees
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in breadth, and thoſe reflected from the other of twenty degrees,
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but ſeen by compreſſion, under the quantity of four degrees: and
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ſuch a ſituation ſhall the eye obtain, when it is placed between the
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ſaid Hemiſphere, and the body which illuminates it; for then the
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ſight and rayes move in the ſame lines. </
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<
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>It ſeemeth not impoſſible
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therefore, but that the Moon may be of a very equal ſuperficies;
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and that nevertheleſſe, it may appear when it is at the full, no leſs </
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