.Ml;. H. X. DICKSOX OX THE CIKCl'EATIOX OE THE 
1 Hi 
in September pressure Is somewhat above the average south and south-west of the 
British Isles, l)ut below it over Norway, a phase which would increase the strength 
of the westerly winds, but which is quickly modified by the spreading northward 
the relatively high pressure over nearly the whole of Western Europe, while further 
west ])ressure keeps to the average, or falls a little below it. The gradients are thus 
stronger than usual for southerly winds, and the “ north-and-south ” form of tlie 
winter drift circulation becomes S 2 )ecially well marked. 
The circulation of waters in the No]Th Atlantic therefore not only follows the 
general seasonal changes in the atmospheric circidatlon, but tlie irregularities in the 
seasonal changes, which in these latitudes may amount to a large fraction of the 
whole, are acconq)anled by irregular variations in the oceanic streams, also amounting 
to large changes in tlie total movement: the oceanic changes bear similar relations to 
tlie atmospheric in both cases. The effect of changes in the direction and force of 
prevailing winds makes itself felt almost Immediately on the “ drift ” circulation, 
wliile the relief currents produced by tlie lianking-up of water are longer in responding, 
and “thermal” currents due to melting of ice liv warm water below the surface take 
longer still. The difference in the time-interval arising in this way must lead to 
a smoothing out of the effects on the deeper movements of water, and it is probably 
onl}^ when unusual conditions pei'sist for a long time, as in the case of the Atlantic 
anticyclone during 189G, that there is any considerable variation in them. 
The principal conclusions may therefore be summed up as follow’s : — 
1. The surface waters along the whole of the eastern seaboard of North America 
north of (about) lat. 30° N., consisting partly of water brought from the equatorial 
currents by the Gulf Stream and parth'" of water lirought down by the Labrador 
current, are drifted eastwairl aci'oss tlie Atlantic towards south-western Europe, and 
banked up against the land outside the continental shelf(48). This continues all the 
year round, but it is strongest in summer, when the Atlantic anticyclone attains its 
greatest size and Intensity ; and the propmdion of Gulf Stream water Is greatest at 
that season. 
2. The drifts in tlie northern })art of the Atlantic area are under the control of the 
cyclones crossing it. The circulation set iqi accordingly reaches its maximum intensity 
In winter, and almost dies out In summer. In the winter the drifts tend to be south- 
eastw^ard from the mouth of Davis Strait, eastward in mid-Atlantic, and north¬ 
eastward in the eastern region. In spring and autumn the movement is more easterly 
over the wliole distance, and a larger quantity of water from the Labrador current is 
therefore carried eastward. 
3. The water banked up in the manner described in (l) escapes partly downwards, 
partly southwards, and jiartly northwards. It occupies the whole of the eastern 
basin of the North Atlantic, and to the north it extends westward to Davis Strait, 
being confined below 300 fathoms dejith by the ridges connecting Europe, the 
Faeroes, Iceland, and Greenland. Above that level it escapes northward by a strong 
