Dee's principal study in early life lay in astrology; and accordingly, upon the accession of Elizabeth, Robert Dudley, her chief favourite, was sent to consult the doctor as to the aspect of the stars, that they might fix on an auspicious day for celebrating her coronation. Some years after, we find him again on the Continent; and in 1571, being taken ill at Louvaine, the queen sent over two physicians to attend him. Elizabeth afterwards visited him at his house at Mortlake, to view his collection of mathematical instruments and curiosities; and about this time employed him to defend her title to countries discovered in different parts of the globe. He says of himself, that he received the most advantageous offers from Charles V., Ferdinand, Maximilian II., and Rodolph, emperor of Germany; and from the czar of Muscovy an offer of 2000_l._ per annum, on condition that he would reside in his dominions. Had Dee gone no further than this, all would have been well; but he was ruined by his enthusiasm; he dreamed perpetually of the philosopher's stone, and was haunted with the belief of intercourse with spirits. One day in November, 1582, he tells us that as he was at prayer, there appeared to him the angel Uriel at the west window of his museum, who gave him a translucent stone, or crystal, of a convex form, that presented apparitions, and even emitted sounds; so that the observer could hold conversations, ask questions, and receive answers from the figures he saw in this _mirror_. With this speculum, black-stone, or show-stone, Dee used to "call his spirits," and Kelly, his associate, "did all his feats upon." Kelly, who acted as seer, reported what spirits he saw, and what they said; whilst Dee, who sat at a table, recorded the spiritual intelligence. A folio volume of their notes was published by Casaubon; and many more, containing the most unintelligible jargon, remain in MS. in the British Museum, together with the consecrated cakes of wax, marked with mathematical figures and hieroglyphics, used in their mummeries. At length, Dee fell into disrepute; his chemical apparatus, and other stock in trade, were destroyed by the mob, who made an attack upon his house; but the mirror is stated to have been saved. It subsequently passed into the collection of the Mordaunts, Earls of Peterborough, in whose catalogue it is called _the black stone, into which Dr. Dee used to call his spirits_. From the Mordaunts it passed to Lady Elizabeth Germaine, and from her to John, Duke of Argyle, whose son, Lord Frederick Campbell, presented it to Horace Walpole; and on the breaking up of the collection at Strawberry Hill in 1842, this precious relic was sold: it was described in the catalogue as "a singularly interesting and curious relic of the superstition of our ancestors on the celebrated speculum of Kennel coal, highly polished, in a leathern case."