The Optical World of William Gascoigne
During Gascoigne’s lifetime the science of optics was in its infancy. Great strides had been made in the Middle Ages by arab scholars, such as Ibn Is-haq (al-Kindi) and Ibn al-Haitham (Alhazen), in understanding the nature of vision, but at the dawn of the seventeenth century the subject of lenses and mirrors was still largely the domain of craftsmen. The making of lenses for spectacles—progressing through trial and error—was the subject of family secrets. When Galileo turned a telescope to the heavens in 1610, however, discovering the craters and mountains of the Moon, the satellites of Jupiter, and the crescent phases of Venus, everything changed. The secrecy was still present—indeed, not until 1638, as his eyesight began to fail, did Galileo privately reveal (to Mariani) his own method of grinding and polishing lenses—but the quest to understand the behaviour of optical systems gained a new impetus. Dioptrics—the theory of lens-based image formation—and catoptrics—that of mirror-based systems—began to make real progress.