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JESUITICA: A man of vision

scheiner_01One of the treasures in Dublin’s Marsh’s Library is an early edition of  Oculus, hoc est, by Christoph Scheiner (1575-1650), a German Jesuit who showed for the first time a diagram of the optic nerve entering the eyeball at one side. He constructed a model which represented the eye by a camera obscura with a spherical glass retina, a lens and cornea and aqueous and vitreous humours. He described the principle of accommodation (by which the focal length of the eye changes) in a way that has remained fundamentally unchanged since his time. Even before this pioneering work on the eye, Scheiner was famous as the inventor of the Pantograph (an early duplicating machine), and as a meteorologist who wrote the standard work on sunspots.