topic form, for instance, alvimlnum. Others such 

 as the element tin, exists in 10 isotopic forms, 

 one of which is a radioisotope. (39) 



ISOTOPE POWER GENERATORS. See SNAP. 



ISOTROPIC . Having the same physical properties in 

 all directions; isotropous. (17) 



ISRU. International Scientific Radio Union. 

 ISS . International Seisraological Summary. 



ISTHMUS . A narrow strip of land connecting two 

 larger portions of land. A submarine elevation 

 joining two land areas separating two basins or 

 depressions by a depth less than that of the 

 basins is called a submarine isthmus. (17) 



ITTC. Inter-American Tropical Tuna Commission. 



ITU . International Telecommunications Union. 



lUB . International Union of Biochemistry. 

 lUBS . International Union of Biological Sciences. 



lUG . International Union of Geography. 



lUGG . International Union of Geodesy and Geo- 

 physics . 



lUGS . International Union on Geological Sciences. 



lUPAC . International Union of Pure and Applied 

 Chemistry. 



lUPAP . International Union of Pure and Applied 

 Physics . 



lUPS . International Union of Physiological 

 Science. 



lURS. International Union of Radio Sciences. 



IWC. International Whaling Commission. 



Established December 1946 under the Inter- 

 national Whaling Convention of November 1948. 



Activities: Conserves the remaining world 

 whale stocks, encourages studies of whale popula- 

 tions, collects statistical information, studies 

 methods of maintaining and increasing the whale 

 population. The Commission meets annually to carry 

 out its functions of reviewing reports and issuing 

 such regulations as seem necessary. Annual reports 

 are published and there is some participation in 

 whale tagging studies and research programs. Most 

 of the research activity is supported directly by 

 member countries . 



Membership: Australia, Brazil, Canada, Den- 

 mark, France, Iceland, Japan, Mexico, Netherlands, 

 New Zealand, Norway, Panama, ^T.Torfon^ iTm'nn nf qnnfh 

 Africa, United Kingdom, U.S.S.R., United States. 



JAN. Joint Army-Navy. 



JAPAN CURRENT . See KUROSHIO CURRENT. (24) 



JCAR . Joint Commission of Applied Radioactivity. 



JELLYFISH . Common name for medusoid coelenterates ; 

 they are semitransparent, pelagic, tentacled inver- 

 tebrates. Some species have venom cells in their 

 tentacles; some species are capable of producing 

 a glowing-ball type of bioluminescence. (15) 



JETTY . United States terminology . A structure, 

 such as a wharf or pier, so located as to influence 

 current or protect the entrance to a harbor or 

 river. A jetty extending into the sea to protect 

 the coast from erosion is called a GROIN. A jetty 

 which breaks the force of the sea at any place is 

 called a BREAKWATER. A jetty wall, or bank, often 

 submerged, built to direct or confine the flow of 

 a river or tidal current is called a training wall. 

 A wall or embankment along a waterfront, to resist 

 encroachments of the sea, is called a sea wall. 

 British Terminology . A pier, usually of solid con- 

 struction, intended as a berthing place for vessels. 

 See DOCK, LANDING, WHARF. (17) 



JHO . Japan Hydrographic Office. 



JMA . Japan Meteorological Agency. 



JETTISON . The throwing overboard of objects, 

 especially to lighten a craft in distress. Jet- 

 tisoned objects that float are termed flotsam; 

 objects that sink, jetsam; and heavy articles that 

 are buoyed for future recovery, lagan. (17) 



JETSAM . See JETTISON. 



JUNCTION BUOY . A buoy marking the junction of two 

 channels or two parts of a channel when proceeding 

 from seaward. The opposite is bifurcation buoy. 

 (17) 



JURY RIG . Any temporary or makeshift device, rig, 

 or piece of equipment. 



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