Heliostat. Instrument used in hydrographic surveying for reflecting Sun's rays at one observation station to another at distances up 40 miles or so. Used when direct observations and identification of the station are not possible. 'Heliograph.'
Helm. Tiller by which a rudder is controlled. Also applied to the machinery by which a rudder is controlled, and to the duty of controlling it.
Helmet. Brass cover over a compass carried in a binnacle. Usually carries the lighting arrangements.
Helm Indicator. Pointer geared to steering wheel and moving over a graduated arc to indicate amount of helm being used, and angular position of rudder.