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, thèse 

 samples, after the température is recorded, being reserved for 

 subséquent analysis at the shore laboratory. The chief routine 

 détermination 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 hydrographie 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 

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

 made by the varions national laboratories, and the préparation 

 of the hydrographie tables. The observed and calculated 

 températures and salinities are sent to the Bureau of the 

 International Council for publication (Bulletin des Résultats). 



Records are made on the charts of the areas under 

 investigation, and in this way synoptical représentations of 

 the hydrographie condition of the sea are prepared. Thèse 

 charts of températures and salinities are pictorial représenta- 

 tions of the circulation of the waters of the North Atlantic 

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

 immédiate cause of the water movements in the North Atlantic 

 is the Gulf Stream circulation, which undergoes a periodic 

 expansion and contraction. Thèse gigantic annual pulsations 

 are directly connected with the hydrographical phenomena of 

 the seas of Northern Europe and the climate of tiie British 

 Islands and Western Europe. A periodic flooding takes place 



