PHOTO: TOPFOTO/ALAMY STOCK PHOTO

After inventor Thomas Barlow labored for more than a decade on his orrery – a mechanical model of the solar system – his son Milton displayed a version at the International Exposition of 1867 in Paris. Made of wood, glass, and filigreed cast iron, the 13-foot-diameter device could be programmed to show the precise location of the sun, Venus, Mercury, Earth, and the moon on any day in the 19th century. Thousands of visitors delighted at the device, including Emperor Napoleon III. After the fair, Milton sold variations of the mechanism for up to $2,000 apiece, or roughly $37,000 today.