Water Hammer

—A noise resembling the blows of a hammer, caused by the pulsative action of entrained water within a steam pipe. It is very dangerous, pipes being ruptured at bends, ete., by the force of previously condensed water driven against them when steam is admitted. Water Jet Arrester. A fcrm of lightj ning arrester sometimes used in water power electric plants. It may consist either of a jet of water playing upon a conductor connected to the lines, or a column of water contained in an insulated ~ pipe, and connected at one end to the earth and at the other to the line. It affords a better protection against static charges than against lightning because of high resistance.