It is likely that Heydinger was the librarian who began the great work of organising Henry Cavendish's library, assigning shelfmarks and constructing the impressive catalogue that now resides at Chatsworth. It is organised by theme with the three largest sections appearing first: Astronomy, Mathematics and Natural Philosophy. This mode of organisation confirms what we already know about Henry Cavendish and his primary interests for this was the man who discovered hydrogen in 1766, 'weighed the world' in 1798, and through experiments that he kept virtually secret until his death explained a whole range of phenomena in the fields of electricity, chemistry and magnetism years before anyone else.
Other notable categories in his catalogue include large sections on Natural History, Voyages and Travels, Maps and Geography. This sheds light on a less well-known facet of Henry's life: his pioneering interest in mineralogy, geology and travel at home and abroad.
Written in the last five years of the eighteenth century, the catalogue containing c.9,000 titles (12,000 volumes) is likely to be incomplete as Henry would live and accumulate works for at least ten more years after this point. Upon his death the collection passed to Lord George Cavendish who gifted them to his nephew, the Sixth Duke of Devonshire. The books were first moved to the Oak Room at Chatsworth before being placed in the newly created library of the Sixth Duke, probably in the 1820s or early 1830s.
To quote the account of the Sixth Duke:
This room [the Oak Room], supported by props and furnished with temporary shelves, first received Mr. Cavendish's library, presented to me by my uncle, Lord George Henry Cavendish, when he got the rich inheritance from that philosopher—the man who weighed the world, and buried his science and his wealth in solitude and insignificance at Clapham.
And here they remain today, many in the precisely the same location laid out by the Duke nearly 200 years ago. Taken together they count for around a quarter of the total collection.
|Extract from Henry Cavendish catalogue showing entry for Tabulae motuum coelestium perpetuae (1632), a collection of astronomical tables by Dutch astronomer Philips van Lansbergen. Note the shelfmark: D1-3.|
 Christa Jungnickel and Russell McCormmach, Cavendish: The Experimental Life (Bucknell: Lewisburg, Pennsylvania, 1999), p. 321.
 William Spencer Cavendish, Sixth Duke of Devonshire, Handbook of Chatsworth and Hardwick (London: Privately Printed), p. 21.