Dee straddled the worlds of science and magic. One of the most learned men of his time, he had lectured to crowded halls at the University of Paris when still in his early twenties. He was an ardent promoter of mathematics, a respected astronomer and a leading expert in navigation, having trained many of those who would conduct England's voyages of discovery. At the same time, he immersed himself deeply in Christian angel-magic and Hermetic philosophy, devoting the last third of his life almost exclusively to these pursuits. For Dee, as with many of his contemporaries, these activities were not contradictory, but particular aspects of a consistent world-view.