The commerce of books accosteth and secondeth all my course, and everywhere assisteth me. It comforts me in age, and solaces me in solitarinesse. It easeth me of the burden of a wearysome sloth, and at all times rids me of tedious companies. It abateth the edge of fretting sorrow and...is the best munition I have found in this human peregrination.

Montaigne, Essays (Florio)

The account of the library at Mortlake as it was when Dee left it in 1583, forms one of the most valuable parts ofthe Compendious Rehearsall. Comparing it with the catalogue which he made before leaving with Laski, we can see at a glance of what intrinsic value was this collection of precious books which so often haunted its owner in his dreams. Two original copies of the Catalogue of manuscripts remain, one of which is dated September 6,1583, a fortnight before he sailed from England, and there is a third, made by Ashmole from one of these.

The library contained, however, not only books and manuscripts, to the number of four thousand, bound and unbound, but scientific instruments collected from several parts of Europe. The books alone Dee valued at £2,000 in the current value of the day, for many of them were unique autographia of famous and rare authors. As a further proof of this estimate, he cited to the two Commissioners a great volume in Greek, two others in French, and a third in High Dutch, which together cost him, and his friends for him, £533, as the endorsements upon them will show.

The instruments included a valuable quadrant, used and he says made, by his friend, Richard Chancellor, the navigator to Russia and the White Seas. It measured five feet in semi-diameter, and Dee relates that Chancellor and he together made observations of the sun's height at meridian with it, before this exploring seaman sailed on his last voyage (in which he and his crew perished) in 1556. Many years after, the quadrant was repaired and re-engraved by Mr. Bromfield, the Lieutenant of Ordnance who had given it to Dee, at a cost of £20. On Dee's return to Mortlake, he found it barbarously hacked to pieces with hammers.

There was also a ten foot radius Astronomicus, (some early form of telescope), its staff and cross divided with equal markings, like Chancellor's quadrant. It swung in a frame, and could be easily directed to any point in the heavens, or used for mensuration on the earth.

A couple of globes of Gerard Mercator's best make were among the most valuable contents of the library, especially as upon the celestial globe Dee had marked his own observations of comets, their place and path in the heavens. There were other objects which Mercator had constructed specially for Dee, vis., three theorics, two with horizon and meridian lines in copper. A number of compasses of many kinds were among the objects, for Dee had invented, as we have seen, what he calls a "Paradoxall Cumpass." There was also a great piece of load-stone, or "magnes-stone," of extraordinary virtue. It had been sold for five shillings, but "being divided up and parted with piece-meal it made more than £20."

"There was also an excellent watch-clock, made by one Dibbley, a noteable workman, long since dead, by which clock the tyme might sensibly be measured inteh seconds of an houre, that is, not to faile the 360th. part of an houre. The useof this clock was very great, more than vulgar."

Then in the three laboratories, the chambers and garrets, were stores of "chemical stuff," which he had been twenty years getting together. Also a great cart-load of special vessels for chemical use, some earthen, some of glass, metal and mixed stuff, which he had brought from Lorraine when Mr. Powell and he had gove over in 1571. Of these, only a few broken bits remained. He describes other things left in his other or "open" library, and in particular a "great bladder with about four pounds weight of a very sweetish thing, like a brownish gum in it, artificially prepared by thirty tymes purifying it; whosoever came by it hath more than I could well affoord him for one hundred crownes, as may be proved by witnesses yet living."