In August 1609, Galileo Galilei presented his latest telescope to the public – an instrument built using pre-made spectacle lenses that boasted an approximate magnification of 8x. Although it was effective, Galileo was determined to improve on the design; however, the only way to do so would be to take full control and make his own lenses. The shopping list seen here (and translated below) written by Galileo on the back of a letter dated November 23 1609, shows, among other items, the equipment needed for such an endeavour. In January 1610, he wrote a letter in which he announced the discovery of Jupiter’s moons, spotted thanks to improvements to his telescope.