Calculating specific gravity

Codex Madrid I, folio 33r

After studying Archimedes, Leonardo invented a device to measure specific gravity by water displacement. To make his apparatus he would have visited a slaughterhouse to obtain ox intestine, and then he provided support using iron wire. He measured the specific gravity of lead as 12 (actual value: 11.4). Today we define specific gravity as the ratio of the density (i.e. mass of a unit volume) of a substance to the density of water or some other reference substance. When Leonardo did this experiment we believe he was the first person to ever measure the specific gravity of a substance. (The ancient Roman architect Vitrivius tells us the famous story of how Archimedes yelled "Eureka!" after figuring out that a crown had silver in it rather than being pure gold, but this is quite different than Leonardo's calculation of a particular value for the specific gravity of a substance.)