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THE SIDEREAL MESSENGER.
treats of Optics. Reasoning will be able to conclude nothing else but this, that the orb of Venus turns on its own axis with an exceedingly swift rotation, displaying one after another different parts of its surface which are more or less capable of retaining the sun's light.[1] •••••••• But enough of my own conclusions. Let us now hear as an epilogue Galileo's conclusions built up out of all the observations which he has made with his telescope, and announced from time to time. Thus he writes once more:—
Galileo's conclusions with regard to the inherent nature of the brightness of the stars."Illustrissimo e Reverendissimo Signore mio colendissimo.
"IIo ricevuto gusto, e contento particolarissimo nella lettura dell' ultima di Vostra Signoria Illustrissima e Reverendissima delli 7 stante, ed in particolare in quella parte dove ella m'accenna la favorevole inclinazione dell' Illustriss. Sig. Cons. Wackher, verso- ↑ The first scientific determination of the period of the rotation of Venus was made by Dominique Cassini in 1666, from observations of spots on the planet, and concluded to be about 24 hours; but in 1726 Bianchini deduced a period of 24 d. 8 h. from similar observations. The true period is considered to be 23h. 21 m., determined by Schroeter by a series of observations lasting from 1788 to 1793 on the periodicity of the deformation of the horns of Venus.—(Arago, Astronomie Populaire, 1854.)
Kepler's statements can only be regarded as anticipations of phenomena not yet actually observed.
