THE SIDEREAL MESSENGER.
79
In the preface to Kepler's Dioptrics there are introduced letters of Galileo about the new and astonishing discoveries which he had made in the heavens by the aid of the telescope since the publication of his work, The Sidereal Messenger. The portion of the preface which refers to Galileo, containing these letters and Kepler's remarks upon them, is added here, as continuing the original account of Galileo's astronomical discoveries.
Extract from the Preface of Kepler's Dioptrics.
Augsburg, 1611.
Kepler remarks on the importance of the application of the telescope to astronomical investigations as indicated by Galileo's discoveries published in his Sidereal Messenger."
The Sidereal Messenger" of Galileo has been for a long time in everybody's hands, also my "
Discussion, such as it is,
with this Messenger," and my
Brief Narrative in confirmation of Galileo's
Sidereal Messenger, so any reader may briefly weigh the chief points of that
Messenger and see the nature and the value of the discoveries made by the aid of the telescope, the theory of which I am intending to demonstrate in this treatise. Actual sight testified that there is a certain bright heavenly body which we call the Moon. It was demonstrated from the laws of optics that this body is round; also Astronomy, by
