System of Astronomy, on the Principles of Copernicus

Whilst the greatest effort has been made to ensure the quality of this text, due to the historical nature of this content, in some rare cases there may be minor issues with legibility. To a spectator at the sun the planets would appear to move in harmonious order from west to east; he would probably take the period of Mercury as a standard for comparing the periods of planets; the paths ofthe planets would seem to cross each other.