275 GLOSSARY GLOSSARY Halocline: The horizontal interface between waters of different salinities, especially between fresh water and salt water. Heading: A navigational course followed or to be followed. Henry’s Law: The amount of gas that will dissolve in a liquid at a given temperature is almost directly proportional to the partial pressure of that gas. Holdfast: A rootlike structure that secures algae to the bottom. Hookah diving: Diving with air supplied via an umbilical hose to the surface. Hyperbaric chamber: A pressure vessel used to treat divers with decompression illness. Hydrostatic test: A pressure expansion test for scuba cylinders. Humidity: The amount of water vapor in a gaseous atmosphere. Hypolimnion: The colder layer of water below a thermocline in freshwater. I Inert: A substance which does not normally combine with other substances. Inflatable boat: A fabric-type craft that is filled with air. Ingassing: The process of gas dissolving into a liquid. Integrated regulator: A scuba regulator that is incorporated into an item of diving equipment such as a BC low pressure inflator. Isotherm: A line on a chart linking areas of equal temperature. J J valve: Scuba cylinder on/off valve with reserve mechanism. Jackstay search pattern: A search method using a grid pattern of parallel lines. K K valve: Scuba cylinder on/off valve. Kelp: A giant brown algae that reaches heights of nearly 30 m (100 ft). Kick cycle: The time from when a fin kicks downward during a flutter kick until that same fin kicks downward again. Kinetic theory of gases: The basic explanation of the behavior of gases under all variations of temperature and pressure. L Leeway: Side-slippage in the direction of a current when moving across the current. Lift bag: Underwater container used for buoyancy in lifting objects. Littoral: Pertaining to a sea shore, such as a littoral current. Longshore current: A current flowing along the shore near the surf zone and caused by surf approaching the shore at an angle. Low pressure inflator: A valve on a buoyancy compensator which controls low pressure air from a scuba regulator and can be manually opened to inflate the BC. Lubber line: A fixed reference line on a compass. M Magnetic North: A point near the Arctic Circle towards which a magnetic needle points. Manifold: A high pressure connecting pipe between two or more gas cylinders.
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