484 Mr. H. X. Dickson. The Circulation of the 



"The Circulation of the Surface Waters of the Xorth Atlantic 

 Ocean." By H. K DiCKSOX, B.Sc. Communicated by Sir 

 John Mueeay, K.C.B., F.E.S. Pteceived March 23, — Eead 

 May 17, 1900. 



(Abstract.) 



In this paper an attempt is made to investigate the normal circula- 

 tion of the surface waters of the Atlantic Ocean north of 40^ N. lat., 

 and its changes, by means of a series of synoptic charts sho"snng the 

 distribution of temperatm-e and salinity over the area for each month 

 of the two years 1896 and 1897. 



The temperature observations discussed (nimibering over 16,000) 

 were obtained from the meteorological and hydrographical departments 

 of the coimtries bordering on the North Atlantic, and special arrange- 

 ments were made with the officers of a number of ships for the con- 

 tinuous supply of samples of surface waters for analysis. 



The salinity of the samples obtained was determined by volumetric 

 estimations of the amomit of chlorine present. Over 4,000 samples 

 were dealt with in this way, and special attention was devoted to 

 ascertaining the accuracy of the methods employed. A large number 

 of estimations were also made of sulphates present in the waters, and 

 the -limits of variation from a definite ratio of chloride salinity to 

 sulphate salinity determined. 



The specific gravity of over 500 of the samples was determined with 

 the pyknometer, and a formula connecting the results of these deter- 

 minations with the salinities derived from chlorines investigated. 



The numerical results of the chemical and physical determinations 

 are exhibited in a table, forming a substantial addition to the material 

 available for the discussion of oceanographical problems of this kind. 



The principal conclusions arrived at with reference to the circulation 

 may be summed up as follows :" — 



1. The siuiace waters along the whole of the eastern seaboard of 

 North America north of (about) lat. SO'' N., consistmg partly of water 

 l^rought from the equatorial ciurents by the Gulf Stream, and partly 

 of water brought down by the Labrador current, are drifted eastward 

 across the Atlantic towards south-western Eiu'ope, and banked up 

 against the land outside the continental shelf. This continues all the 

 year round, but it is strongest in summer, when the ^Atlantic anti- 

 cyclone attains its greatest size and intensity ; and the proportion of 

 Gulf Stream water is greatest at that season. 



2. The drifts in the northern part of the Atlantic area are under the 

 control of the cyclones crossing it. The circulation set up accordingly 

 reaches its maximum intensity in winter, and almost dies out in 

 summer. In winter the drifts tend to the south-eastward fromTthe 



