Horologium

(1) Sundials preceded all other instruments for the measurement of time. The gnomon or stocheion of the Greeks was a perpendicular staff or pillar, the shadow of which fell upon a properly marked ground; the polos or helio trop i on consisted of a perpendicular staff, in a basin in which the twelve parts of the day were marked by lines. (2) The clepsydra was a hollow globe, with a short neck, and holes in the bottom; it measured time by the escape of water, and was at first used like an hour-gla to regulate the length of speeches in the A then i an courts. The escape of water was stopped by inserting a stopper in the mouth, when the speaker was interrupted. Smaller clepsydrata made of gla and marked with the hours were used in families. A precisely similar history applies to the horologia of Rome.