Pioneers of Science

61 Cygni appeared astronomical attraction axis body calculated CALIFORN called cause centre centrifugal force century circle comet Copernican Copernican system Copernicus Descartes description of areas diagram diameter direction discovered discovery distance earth earth's orbit ecliptic ellipse equant equator excentricity fact feet force acting Galileo gravity Halley heavens Hence Herschel Hipparchus humps hypothesis instruments inverse Jupiter Jupiter's Kepler Kepler's third law known Laplace LECTURE libration light lunar Mars mass mathematical matter Mercury meteors method miles moon moon's motion moving nebulæ Newton observatory observed ocean once optics orbit parallax period perturbations planet planetary precession Principia Ptolemaic system pull revolution revolve round rotation round the sun satellites Saturn scientific seems seen solar system speed sphere stars supposed telescope theory things third law thought tidal tides tion truth universe Uranus velocity visible whirled whole William Herschel