Nilometer,

Nilometer, an arrangement for measuring the height of the Nile in Egypt. On the island of Rhoda, opposite to Cairo, is a square well, connected with the river by a canal, and containing a graduated marble pillar, divided into 24 cubits, each measuring 21.386 inches. A rise of 18 cubits is traditionally regarded as the height of the lowest inundation; 19 cubits is considered tolerable, 20 excellent, 21 adequate, and 22 complete, but 24 is ruinous. The ordinary maximum of the rise at Cairo is stated at from 24 to 26 feet. For the inundations from 1849 to 1878, see Nature, vol. xxv. The nilometer of Rhoda was constructed during the reign of the calif Al-Mutawakkil, in the year 847. Anciently there seem to have been various nilometers of different kinds, all along the river, as at Memphis (probably the oldest), Ekhmin, Elephantine, and elsewhere.