has been developed by the Survey to extend offshore hydrographic 

 surveys beyond the hmits of Shoran. This equipment was tested under 

 service conditions in 1947, and distances up to 225 miles from shore 

 have been measured. 



The new distance-measuring devices will make possible more rapid 

 extension of offshore surveys and more accurate oceanographic investi- 

 gations in the regions of the continental shelves and beyond. 



Tide and Current Work 



The programme of collecting, analysing, and publishing tide and 

 current data for the Pacific area was considerably expanded since 1939. 

 Two factors contributed to this stepped-up programme. The war in 

 the western Pacific being largely amphibious in nature, our armed forces 

 required information on tides and currents for their over-all planning. 

 As a result, numerous tide gauges were established and current surveys 

 conducted in strategic areas, and a large number of special predictions 

 were prepared. The accumulation of tidal observations has been 

 analysed harmonically and constants determined for 144 places in the 

 Pacific Ocean. 



Much of this material has now been incorporated into the tide and 

 current tables. Special tide and current tables are still being published 

 for the Philippine Islands as well as for Japan and China. For 1949 the 

 tables, together with the regular tide tables for the Pacific and Indian 

 Oceans, contain daily tide predictions for 104 places and tidal difterences 

 for about 2,500 places, as compared with 49 and 1,800 respecti\"ely for 

 1939. Daily current predictions have been added for thirteen places. 



The second factor responsible for the increase in the tidal work of 

 the Bureau has been the programme of co-operation with the Latin 

 American countries, inaugurated in 1941, and with other Government 

 agencies in the western Pacific. The Bureau is now maintaining forty- 

 eight automatic tide gauges in the Pacific. The accumulation of tidal 

 data will not only provide much-needed original information for the 

 prediction of tides, but will contribute greatly to the development of 

 tidal knowledge in the Pacific. 



A comprehensive current survey of Puget Sound, using the newly- 

 developed radio current meter, furnished the basic material for two 

 recently published tidal current charts for the northern and southern 

 parts of the Sound. A number of current surveys were made in San 

 Francisco Bay and in Alaskan waters. A revised edition of Tidal Current 

 Charts, San Francisco Bay, and a pamphlet based on five months of 

 current observations in San Pedro Channel, California, were issued. 

 Comprehensive current surveys of the various passes along the Aleutian 

 Island chain and of the passages through the San Juan Archipelago 

 in Washington are planned. 



Since 1943 the Coast and Geodetic Survey has been systematically 

 making observations for temperature and density of sea-water at most 

 of its tide stations. Publications giving the results of these obser\ations 

 are revised every two years. 



Studies are under way for the development of a general warning 

 system for seismic sea waves. Three steps have thus far been taken : 

 a chart has been published showing the time required for a seismic sea 

 wave to reach Honolulu from an earthquake epicentre in the Pacific ; 

 a local sea- wave detector, which utihzes the arrival of the first part of 



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