2781329 The Heliostat (engraving) by English School, (19th century); Private Collection; (add.info.: The Heliostat, placed on a shelf outside the window, reflecting the ray of light which passes through a hole in a shutter on to a prism, to show the decomposition of light. Illustration for Cyclopaedic Science Simplified by J H Pepper (Frederick Warne, 1869).); 穢 Look and Learn.