58 A TEXTBOOK OF OCEANOGRAPHY 



each line a number of " stations " were selected. A station 

 is a stopping-place for the exploring vessel at which the 

 observations are made and the samples collected. The chart 

 (Fig. 8) shows the lines investigated by the Lancashire Fishery 

 Committee's steamer in the Irish Sea in 1909, with the obser- 

 vation stations numbered serially. 



On reaching the station the steamer is stopped, a sounding 

 made with the Lucas sounding machine, a sample of water is 

 collected from the surface and at intermediate depths, these 

 samples, after the temperature is recorded, being reserved for 

 subsequent analysis at the shore laboratory. The chief routine 

 determination is that of salinity calculated from the amount of 

 chlorine per 1,000 parts of water as found by titration. The 

 halogens are precipitated by nitrate of silver, and the total 

 solids in solution calculated by means of hydrographic tables. 

 The highest degree of accuracy is. necessary, and this is only 

 possible by means of control analyses made at the central 

 laboratory at Christiania. The principal functions of this 

 institution are the supply of instruments of research, the 

 preparation of " standard " sea-water for checking the analyses 

 made by the various national laboratories, and the preparation 

 of the hydrographic tables. The observed and calculated 

 temperatures and salinities are sent to the Bureau of the 

 International Council for publication (Bulletin des Resultats). 



Records are made on the charts of the areas under 

 investigation, and in this \vay synoptical representations of 

 the hydrographic condition of the sea are prepared. These 

 charts of temperatures and salinities are pictorial representa- 

 tions of the circulation of the waters of the North Atlantic 

 Seas from season to season and from year to year. The 

 immediate cause of the water movements in the North Atlantic 

 is the Gulf Stream circulation, which undergoes a periodic 

 expansion and contraction. These gigantic annual pulsations 

 are directly connected with the hydrographical phenomena of 

 the seas of Northern Europe and the climate of the British 

 Islands and Western Europe. A periodic flooding takes place 



