the Southern and Northern Hemispheres, respectively). 



At one time it was held that this was a con- 

 vergence line along its entire extent. It is now 

 recognized that actual convergence occurs only 

 along portions of the line. 



2. Same as METEOROLOGICAL EQUATOR. (14) 



INVERTED ECHO SOUNDER . This instrument is pri- 

 marily designed to provide a continuous and precise 

 measurement of the depth of other instruments, such 

 as the velociraeter being lowered along with it into 

 the sea. The device is also used for detailed sur- 

 vey of the ocean bottom in deep water and by simple 

 alteration of its suspension can be used for high 

 powered short pulse echo ranging. 



The device consists of a high powered "pinger" 

 as a short pulse transmitting unit mounted along- 

 side a sensitive fixed tuned receiver. Both units 

 are connected to a common transducer which is used 

 both as a projector and as a receiving hydrophone. 

 The apparatus is self-contained and battery operated. 

 (30) 



IN VITRO . In Glass or in a test tube, beaker etc. 



IN VIVO . In a living organism - man, plant or 

 animal . 



lOAN . Institute of Oceanology (Academy of Sciences 

 USSR) . 



lOBC . Indian Ocean Biological Center. 



IOC . Intergovernmental Oceanographic Commission 

 of the United Nations Education, Scientific and 

 Cultural Organization (UNESCO) . 



IPSFC . International Pacific Salmon Fisheries 

 Commission. 



IPY . Inches penetration per year. Usually used in 

 corrosion studies as a means of expressing the loss 

 in thickness in a given period of time. Mp„ = mils 

 penetration per year and M^j^j = milligrams per square 

 decimeter per day loss in weight are also terms 

 used. (35) 



IRMINGER CURRENT . An ocean current that is one of 

 the terminal branches of the Gulf Stream system 

 (part of the northern branch of the NORTH ATLANTIC 

 CURRENT); it flows toward the west off the south 

 coast of Iceland. 



A small portion of the water of the Irminger 

 Current bends around the west coast of Iceland but 

 the greater amount turns south and becomes more or 

 less mixed with the water of the EAST GREENLAND 

 CURRENT. (24) 



IRREGULAR ICEBERG . See PINNACLED ICEBERG. 

 ISA . Instrument Society of America. 



ISAACS HIGH-SPEED SAMPLER. This is a streamlined 



lOE . Indian Ocean Expedition. 



tube containing a net and a depth registering flow 

 meter. Water enters the sampler through a one- 

 inch opening, is filtered by the net, passes around 

 and activates the meter, and is ejected astern. 

 The sampler has been constructed so that it precedes 

 the cable by about a third of its length, thereby 

 more readily capturing everything in its path. A 

 depressor-vane is used to sample at depth. 



This instrument is reputed to capture macro- 

 plankton, be useful at depths to 60 meters, per- 

 form well at high speeds (8 to 12 knots), give 

 a record of both depth and flow, be useful over 

 considerable distances, and be used in series 

 alignment. (35) 



lOF . International Oceanographic Foundation - 

 Institute of Marine Sciences 

 1 Rickenbacker Causeway - Virginia Key 

 Miami, Florida. 

 This organization publishes the "SEA FRON- 

 TIERS" and "SEA SECRETS" magazines and provides 

 active support for scientific research and educa- 

 tion regarding the oceans. 



lOMS . International Organization on Marine 

 Sciences . 



ION. An atom which has lost or gained one or more 

 electrons and is therefore positively or negative- 

 ly charged . (36) 



IONIZATION . The breaking up of atoms into ions. 

 (36) 



IPCEESP . International Permanent Commission for 

 the Exploration and Exploitation of the South 

 Pacific . 



ISAACS -KIDD WATER SAMPLER . The sampler consists 

 essentially of a plastic tube closed off at one 

 end by a plastic disc containing an "o" ring in 

 its inner face. A stainless steel rod orients 

 another plastic disc (the induction plunger), 

 which seals off, when in closed position, the hole 

 through which the rod enters, and positions a 

 plastic plug, containing an "o" ring in its peri- 

 phery, which closes off the open end of the plastic 

 tube. A stainless steel framework supports the 

 tube. Stainless steel springs which operate the 

 closure plug and induction plunger, are attached 

 to the framework at one end. The sampler is acti- 

 vated when the inverting frame is tripped to the 

 upright position. A steel pressure-tight chamber 

 for protecting reversing thermometers at very 

 great depths may be mounted on the inverting frame 

 in place of the water sampler. (30) 



ISABNORMAL . A line connecting points having the 

 same difference from normal, usually temperature, 

 or indicating the same difference between actual 

 and calculated values at different parallels. (17) 



IFFC . The Indo-Pacific Fisheries Council, a 17 

 country intergovernmental organization sponsored 

 by the Food and Agriculture Organization of the 

 United Nations, was established as a result of a 

 meeting held at Baguio, Republic of the Philip- 

 pines, in February 1948. 



IPHC . 'International Pacific Halibut Commission. 



IPMS . International Polar Motion Service. 



IPSE . International Pool of Scientific Equipment. 



ISALLOBAR . A line connecting points having the 

 same change of atmospheric pressure in a specified 

 period. (17) 



IS ALLOT HERM . A line connecting points having the 

 same change of temperature in a specified period. 

 (17) 



ISANOMAL. A line connecting points having the same 

 anomalies of temperature, pressure, etc. (17) 



63 



