On assuming the government of Transcaspia, the Russians made a special study of this all-important question, and came to the conclusion that it was impossible to improve on the methods evolved by ages of practical experience. Their policy, therefore, as regards irrigation, has been one of non-interference. Steps were taken to prevent cultivators in the Persian and Afghan territory from tampering with the sources of the water-supply. A chief engineer is posted at the provincial capital, Askabad, and subordinate ones at the district headquarters; but their functions are limited to suggesting improvements and supervising the repairs to canals and distributories. The task of allotting the water-supply was left in the hands of the Mīrāb,[669] a native official elected by the inhabitants of every village dependent on irrigation. His operations are guided by the average quantity of water required by individual peasants. The unit is termed _Sū_,[670] and is by no means a constant quantity. In some parts it implies the volume of water sufficient to irrigate a given area, varying between one and five acres. In Merv the Sū implies the quantity which flows in two hours through a distributory discharging water at the rate of 1¼ quarts per second. In Tajand it is equivalent to the needs of an average garden, or to a discharge of half a gallon per second. In many parts of the Merv and Akkal oasis the process is simplified by the existence of associations of peasants, termed _Artel_, each of whom receives a _Sarkār_,[671] or head of water, consisting of 8 to 36 Sū. The ordinary irrigation channels are held in common by the villages which they supply, but wells and underground aqueducts vest in the person who excavates them and in his heirs. The Russians have shown great practical wisdom in avoiding unnecessary interference with a system so complex; for an attempt at stringent control would bring them in contact with fierce prejudices and lead to loss of prestige.