"Two years before the publication of his Dioptrics, viz. in 1609, Kepler had given to the world his great work entitle…"

"The figure A D B E [in Figure 9] represents the form of a planetary orbit, which is that of an oval or ellipse. The l…"

"Lagrange, struck with the circumstance that the calculus had never given any inequalities but such as were periodical…"

"The planetary orbits are not exact circles, but are more or less elliptical, the Sun being situated not at the centre…"

"Kepler's observation of the elliptical rotation of the planets was the first of three laws, quantitatively expressed,…"

"If the earth attracts the moon, why does not the moon fall to the earth? A glance at the accompanying figure will hel…"

"Imagine but a single planet revolving about the sun. According to Newton's law of gravitation, the planet's path woul…"

"According to Newton's law an isolated planet in its motion around a central sun would describe, period after period, …"

"Mercury. The inclination and eccentricity of orbit are greater than those of any of the planets. In obedience to Kepl…"

"Parabola, ellipse, hyperbola, and circle are called conic sections, or simply conics, because they can all be obtaine…"