Mean time sundial, 1892.
© Science Museum / Science & Society Picture Library
This azimuth sundial was patented by Major-General J R Oliver in 1892 and made by Negretti and Zambra. It is designed to indicate mean time directly, the equation of time being automatically allowed for by the shape of the style which casts the shadow. Henry Negretti (d 1879) and Joseph Warren Zambra (d 1877) were in partnership from 1850 until the end of the 19th century and sold a variety of scientific instruments.