Types of hygrometers; 18th century; to measure moisture content by Anderson 8; Dr. Robert Hooke 9;10; Dr. Hale 11; James Ferguson 12;13; and Bradford's hydrostatical instrument for weighing coin and checking weight and purity 1-3. Copperplate engraving by Wilson Lowry from Abraham Rees' Cyclopedia or Universal Dictionary of Arts; Sciences and Literature; Longman; Hurst; Rees; Orme and Brown; London; 1819.