Hydrometers, Antique Hydrometers, circa 1909, two intact hydrometers in an original felt-lined wooden box that originally held a set of five (for different proof ranges, which explains the A-E letter prefixes of the serial numbers), the labels are Series 1889 and Series 1909; also incl. two modern intact hydrometers (without stamps), each a different size and proof, very few intact early hydrometers are believed to exist