Galilei, Galileo, The systems of the world, 1661
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              being ſuppoſed, and not granted, that ſome one being placed in the
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              Moon to obſerve the Earth, he would every day ſee the whole
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              Terreſtrial ſuperficies, by means of the Moons going about the
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              Earth in twenty four or twenty five hours; but we never ſee but
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              half of the Moon, ſince it revolves not in it ſelf, as it muſt do to
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              be ſeen in every part of it.</s>
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              <s>SALV. </s>
              <s>So that this, befals not contrarily, namely, that her
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              volving in her ſelf, is the cauſe that we ſee not the other half of
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              her, for ſo it would be neceſſary it ſhould be, if ſhe had the
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              cle. </s>
              <s>But what other difference have you behind, to exchange for
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              this which you have named?</s>
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              <s>SAGR. </s>
              <s>Let me ſee; Well for the preſent I cannot think of
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              any other.</s>
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              <s>SALV. </s>
              <s>And what if the Earth (as you have well noted) ſeeth
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              no more than half the Moon, whereas from the Moon one may ſee
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              all the Earth; and on the contrary, all the Earth ſeeth the Moon, and
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              but onely half of it ſeeth the Earth? </s>
              <s>For the inhabitants, to ſo ſpeak,
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              of the ſuperior Hemiſphere of the Moon, which is to us inviſible,
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              are deprived of the ſight of the Earth: and theſe haply are the
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              Anticthones.
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              But here I remember a particular accident, newly
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              obſerved by our
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              Academian,
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              in the Moon, from whch are gathered
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              two neceſſary conſequences; one is, that we ſee ſomewhat more
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              than half of the Moon; and the other is, that the motion of the
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              Moon hath exact concentricity with the Earth: and thus he finds
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              the
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              Phœnomenon
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              and obſervation. </s>
              <s>When the Moon hath a
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              reſpondence and natural ſympathy with the Earth, towards which
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              it hath its aſpect in ſuch a determinate part, it is neceſſary that the
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              right line which conjoyns their centers, do paſſe ever by the ſame
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              point of the Moons ſuperficies; ſo that, who ſo ſhall from the
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              ter of the Earth behold the ſame, ſhall alwayes ſee the ſame
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              Diſcus
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              or Face of the Moon punctually determined by one and
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              the ſame circumference; But if a man be placed upon the
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              ſtrial ſurface, the ray which from his eye paſſeth to the centre of the
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              Lunar Globe, will not paſs by the ſame point of its ſuperficies, by
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              which the line paſſeth that is drawn from the centre of the Earth
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              to that of the Moon, ſave onely when it is vertical to him: but
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              the Moon being placed in the Eaſt, or in the Weſt, the point of
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              incidence of the viſual ray, is higher than that of the line which
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              conjoyns the centres; and therefore the obſerver may diſcern
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              ſome part of the Lunar Hemiſphere towards the upper
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              rence, and alike part of the other is inviſible: they are
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              ble and undiſcernable, in reſpect of the Hemiſphere beheld from
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              the true centre of the Earth: and becauſe the part of the Moons
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              circumference, which is ſuperiour in its riſing, is nethermoſt in its
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              ſetting; therefore the difference of the ſaid ſuperiour and </s>
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