Compound lever, c 1750.
© Science Museum / Science & Society Picture Library
A lever, one of the 'simple machines' known since antiquity, enables a heavier load to be lifted using a lighter one. This machine uses a series of three levers so that the weight to be lifted can be sixty times greater than the 'power' required to lift it. This instrument belonged to Dr Stephen Demainbray (1710-1782), a science leturer of the 18th century.