An instrument for measuring time by means of a shadow cast by the sun upon a surface properly placed for the purpose. Sun dials are an invention of very great antiquity, and are frequently mentioned in the Bible; and Vitruvius speaks of one made by the ancient Chaldee historian, Berosus, on a reclining plane, almost parallel to the plane of the equinoctial. Before the invention of clocks and watches, dials afforded almost the only means of marking the lapse of small portions of time; and dials were, therefore, generally to be seen in most places of public resort, as churches, crossways, markets, etc.; but since that invention, and the immense improvements made in it, dials have gone gradually into disuse, and are now rarely to be met with in England, where, indeed, the variable nature of the climate materially limits their utility. On the Continent they are still to be met with; and one kind, called the pillar dial, consisting of an elegant stone column, is frequently introduced as an ornament in the squares and market places.

Our ingenious neighbours, the French, have likewise contrived a method of calling attention, at least once in the day, to the silent progress of the shadow over the dial, by means of a small mortar placed on the meridian line of a dial with a burning lens placed over the touch-hole, at such a distance and angle, that as soon as the sun arrives on the meridian, its rays, concentrated by the lens, set fire to the powder, which discharges the gun, and thus announces the hour of noon. "We take no note of time but from its loss; To give it then a tongue is wise in man." Dials of this description are placed in the gardens of the Palais Royal, and of the Luxembourg.