The heliostat takes light from the sun as it tracks across the sky, and redirects it in a fixed direction. To accomplish this, the light is reflected from a mirror that reproduces the motion of the sun, except at twice the rate. Although he did not invent the heliostat, the Dutch physicist William Jacob s'Gravesande gave it first prominence through mention in his 1742 textbook by. He coined the word from the Greek words for “sun” and “stationary.” Pictured is a Silbermann-type heliostat made by instrument manufacturer Duboscq.
Property of the W&L Physics & Engineering Department
“Heliostat,” Digital Exhibits at Washington and Lee University Library, accessed January 22, 2018, http://omeka.wlu.edu/items/show/180.