Treasures of the Bodleian

More than any earlier astronomer, Tycho registered his results systematically, using instruments built to unprecedented specifications. He presented this lavish, hand-coloured copy of his book of astronomical instruments to Grimani, the Doge of Venice, in 1599, as a kind of curriculum vitae. The engraving displayed here shows Tycho in his observatory, next to a large quadrant of his own design. The key printed opposite states: ‘The use of the large quadrant is for determining the altitudes of the stars within one-sixth of a minute, by sighting through the upper and lower slits of one of the pinnules and along the two corresponding sides of the cylinder, and reading off the altitude on the outer rim of the quadrant in accordance with the position of this pinnule.’