David Brewster

Brewster invented the kaleidoscope in 1816 and made almost nothing from it, because the patent was drawn badly enough that copies were on sale across Britain before he could act. The optics behind it were serious work: he established the law now carrying his name, describing the angle at which reflected light becomes fully polarised, and spent decades on the polarisation and absorption of light. He improved the lighthouse lens as well. The biographies are the other half of the career. His Life of Sir Isaac Newton, and the later two-volume Memoirs, were the first biographies to use Newton's own papers, and they are frankly partisan: Brewster defends Newton's conduct in the priority dispute with Leibniz, and plays down both the alchemy and the unorthodox theology he had found in the manuscripts and plainly found uncomfortable. The Martyrs of Science sets Galileo, Tycho Brahe and Kepler together as men punished for what they discovered. Letters on Natural Magic, addressed to Walter Scott, explains apparent marvels as optics and psychology.