The sidereal messenger of Galileo Galilei : and a part of the preface to Kepler's Dioptrics containing the original account of Galileo's astronomical discoveries . hat there is round the body of theMoon, just as round the Earth, an envelope of somesubstance denser than the rest of the ether, which issufficient to receive and reflect the Sun s rays, althoughit does not possess so much opaqueness as to be ableto prevent our seeing through it—especially when itis not illuminated. That envelope, when illuminatedby the Suns rays, renders the body of the Moon THE SIDEREAL MESSENGER. 27 apparently la
The sidereal messenger of Galileo Galilei : and a part of the preface to Kepler's Dioptrics containing the original account of Galileo's astronomical discoveries . hat there is round the body of theMoon, just as round the Earth, an envelope of somesubstance denser than the rest of the ether, which issufficient to receive and reflect the Sun s rays, althoughit does not possess so much opaqueness as to be ableto prevent our seeing through it—especially when itis not illuminated. That envelope, when illuminatedby the Suns rays, renders the body of the Moon THE SIDEREAL MESSENGER. 27 apparently larger than it really is, and would be ableto stop our sight from penetrating to the solid bodyof the Moon, if its thickness were greater; now, it isof greater thickness about the circumference of theMoon, greater, I mean, not in actual thickness, butwith reference to our sight-rays, which cut it obliquely;and so it may stop our vision, especially when it isin a state of brightness, and may conceal the truecircumference of the Moon on the side towards theSun. This may be understood more clearly from theadjoining figure, in which the body of the Moon, A B is surrounded by an enveloping atmosphere, D E eye at f penetrates to the middle parts of theMoon, as at a, through a thickness, da, of the at-mosphere ; but towards the extreme parts a mass ofatmosphere of greater depth, E B, shuts out its boun-dary from our sight. An argument in favour of this 28 THE SIDEREAL MESSENGER. is, that the illuminated portion of the Moon appearsof larger circumference than the rest of the orb whichis in shadow. Perhaps also some will think that this same causeaffords a very reasonable explanation why the greaterspots on the Moon are not seen to reach to the edgeof the circumference on any side, although it mightbe expected that some would be found about the edgeas well as elsewhere; and it seems credible that thereare spots there, but that they cannot be seen becausethey are hidden by a mas
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Keywords: ., bookauthorgalileigalileo1, bookcentury1800, booksubjectastronomy
