442 SOME RESULTS OF THE INTERNATIONAL FISHERY INVESTIGATIONS. 



closed by moans of a " niossenger," wliieh slides down the line carrying 

 Uie bottle. Both central and concentric cbambers are then filled 

 with the water present at the deptii to which the instrument is 

 lowered ; the thermometer registers the temperature of this water in 

 the central chamber, and this being surrounded by three or four 

 concentric shells of water, boat is only very slowly conducted in either 

 direction through these water walls. In hauling the water-bottle the 

 temperature does not, therefore, appreciably rise. These soundings 

 are made for a number of depths, for instance, 5, 10, 20, 50, 100 metres, 

 and the temperatures of these separate water strata are so obtained. 



Each exploring vessel makes one such cruise at regular intervals, and 

 the cruises over all the International area are made as nearly as possible 

 at the same time. At least one cruise is made quarterly, and the 

 months selected are February, May, August, and November. On the 

 return of the vessel to her base, the water samples collected are sent 

 ashore for analysis, and the salinity at least is determined. What is 

 actually done is to estimate the percentage of clilorine (or rather total 

 halogens) present by precii)itating these substances, according to various 

 methods, by nitrate of silver. The total solids in solution are then 

 calculated from the values obtained in the analyses by means of hydro- 

 graphic tables. The highest degree of accuracy is necessary, and this 

 has only been made possible by means of check analyses made by the 

 Central Laboratory, under the control of the International Council. 

 The principal functions of this institution are the supply of the 

 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 results obtained — salinities, temperatures, etc. — are then sent to 

 the Bureau of the International Council to be published in the Bulletin 

 des Ri'suUats. The values are marked on charts of the areas under 

 investigation, so tiiat synoptical representations of tlie hydrographic 

 condition of the sea are prepared. Such charts of temperatures and 

 salinities, prepared for successive years or portions of a year, are pictorial 

 representations of the circulation of the waters of tlie North Atlantic 

 seas. 



The inmiediate cause of these water movements in the North European 

 area is the Gulf Stream circulation. It is now generally known, though 

 one may still find it stated otherwise in the textbooks, that the actual 

 (lulf Stream does not at any time reach the shores of the British 

 Islands. Issuing from the Gulf of IMexico, this great current forms a 

 closed eddy in the North Atlantic Ocean, and its waters circulate round 

 a portion of that sen, cliaracterized by the presence of floating seaweed 

 and a peculiar fauna. Tiiis is the "Sargasso Sea." In 1889 the limits 



