gems, specific gravity, density, history of gemology, Arabic Mineralogy, early lapidaries

Bacon’s History of Dense and Rare (Historia densi et rari), here published in the nineteenth-century collected edition edited by Spedding, Ellis, and Heath, is an experimental and theoretical investigation of density and rarity as fundamental properties of matter. Bacon compares the relative densities of numerous natural and artificial substances and considers how matter expands or contracts through heating, cooling, pressure, solution, and other processes. Of mineralogical and gemological interest are his observations and tabulated comparisons of stones, metals, crystals, and other mineral substances, including attempts to determine their relative weights by displacement and other experimental methods. Written in the early seventeenth century, the work is significant in the history of physical mineralogy because it reflects an early quantitative approach to what would later be formalized as specific gravity, an important diagnostic property of minerals and gemstones.