Universal ring dial, English, 1734-1796.
© Science Museum / Science & Society Picture Library
Made by George Adams of London, this bras dial with silvered scales offers an elaborate example of first clas workmanship and finish. It can be used to find the time of day anywhere in the Northern Hemisphere and indicates the time by a spot of light from the sun pasing through a pin hole and falling upon a scale of hours. The bras slider must first be adjusted to the correct date. Then the main body of the dial is turned within its supporting ring so that the hour circle is at an angle towards the horizon. With the pinhole facing the sun, the whole dial is then rotated until the spot of light falls onto the hour ring, and the time can then be read. This sundial does not require a compas for setting, but will not give an accurate time reading around midday when the sun's altitude above the horizon changes only slowly.