The Portsmouth Collection

Notes, mostly from Berquen, Boethius, Tavernier and Boyle. Index of refraction in diamonds is given 41/100 on the authority of Halley. On p.3 is mentioned a very fragile and soft western Topaz which he found to have a specific gravity 4.27, though the sines of refraction were as 14 to 23 (could this be Baryte?). On p.7 he deduces from the cleavage that gems are crystallized like salts from juices which turn to stone. At the end are the gold and silver standards of different countries.