John Dee's house at Mortlake held something no English institution could match at the time. His library ran to several thousand volumes and manuscripts, at a period when the university libraries held a fraction of that, and it was assembled deliberately across mathematics, navigation, astronomy, medicine, history and the whole body of Renaissance magical and Hermetic writing.
Nicholas Clulee's study of Dee's natural philosophy argues against reading the library as two collections, a respectable one and an occult one, because Dee did not divide them. The mathematics that made him a consultant on navigation for English voyages and the angelic work he pursued in the same rooms rested on one view of a universe organised by number and by descending grades of intelligence, in which a well prepared mind could reach the levels above it.
Scholars came to Mortlake to use the collection, and the queen visited. What happened to it is part of the site's significance too. During Dee's absence on the continent in the later 1580s the house was broken into and the library dispersed, with volumes taken by acquaintances and sold on, and Dee recovered only some of them. A large part of the best equipped private research collection in Elizabethan England is simply gone, and what is known of its contents comes largely from the catalogue Dee himself had made before he left.