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It has not been assumed that the reader's knowledge of mathe maties extends beyond the more rudimentary portions of Geometry, Algebra, and Trigonometry. A knowledge of elementary Dynamics will, however, be required in reading the last three chapters, but all dynamical investigations have been left till the end of the book, thus separating dynamical from descriptive Astronomy. The principal properties of the Sphere required in Astronomy have been collected in the Introductory Chapter; and, as it is impossible to understand Kepler's Laws without a slight knowledge of the properties Of the Ellipse, the more important Of these have been collected in the Appendix for the benefit of students who have not read Conic Sections.
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