178 KEPORT— 1876. 



to propel its warm waters across the Atlantic, have become the controversial field 

 for the upliolders of horizontal and vertical circulation. The one hj'pothesis as- 

 signs to the Gulf-stream all the beneficent power of its genial warmth, extend- 

 ing even beyond the North Cape of Europe, which has been conceded to it from 

 the time of Franklin. The other hypothesis reduces its capacity and power, con- 

 siders that it is disintegrated in mid- Atlantic, and tliat the modified climate we 

 enjoy is brought by prevailing winds from the warm area surrounding the stream ; 

 and to this has been more recently added, '• by the heating-power of a warm sub- 

 surface stratum, whose slow northward movement arises from a constantly re- 

 newed disturbance of thermal equilibrium between the polar and equatorial portions 

 of the oceanic area." 



Without denying the active power of tliis disturbed thermal equilibrium — 

 although in this special case it is an abstraction difficult to follow — and giving due 

 weight to the manj^ cogent facts which have been brought forward in support of 

 both views, there appears to be still a connecting link or links wanting to account 

 for the southern movements of arctic waters; which movements, to me, are even 

 more remarlvable as phj'sical phenomena than the translation of the warm waters 

 from the Gulf-sti-eam area to a high northern latitude. 



This movement of arctic waters is forciblj'' illustrated by the winter drifts down 

 Davis Strait of the ships 'Resolute,' 'Fox,' 'Advance,' and apart of the crew of 

 the ' Polaris,' when enclosed in pack ice, exceeding in some cases a thousand miles; 

 similarly by the winter drift of a part of the German expedition of 1870, down the 

 east side of Greenland, from the latitude of 72° to Cape Farewell. If to these ex- 

 amples we add the experience of Parry in his memorable attempt to reach the 

 North Pole from Spitzbergen in the summer of 18j!7, it must be inferred that a 

 perennial flow of surface-water from the polar area into the Atlantic obtains, and, 

 judging from the strength of the winter northerly winds, that the outflow is pro- 

 bably at its maximum strength in the early months of the year. 



When we further know that the northern movement of warm waters gives in 

 winter a large accession of temperature to the west coast of Scotland, to the Fiiroe 

 islands, and, extending to the coasts of Norway, as far as the North Cape, the con- 

 sideration arises whether this onward movement of waters from southern sources 

 is not the immediate cause of displacement of the water in the polar area and its 

 forced return along the channels indicated by those winter drifts to which I have 

 referred. 



That some unlooked-for and unsuspected cause is the great agent in forcing 

 southern waters into the Atlantic polar basin has long forced itself on my convic- 

 tion ; and I now suspect it is to the cause producing the annual A'ariations in the 

 sea-level (for, as I have mentioned, indications exist of the seas of the northern 

 hemisphere having a higher level in winter thin in summer) that we must direct 

 our attention before thi3 full solution of Ocean Circulation is accepted. 



The facts of the annual changes of sea-level, whatever they may ultimately proA'e, 

 have hitherto ranged themselves as a part of tidal action, and so escaped general 

 attention. Physicists well know the complication of tidal phenomena, and, if one 

 may be permitted to say, the imperfection of our tidal theory ; certain it is that 

 the tides on the ICuropean coasts of the Atlantic are so far abnormal, that one of 

 our best authorities on the subject (Sir William Thomson) describes them (in re- 

 lation, 1 assume, to tidal theory) as "irregularly simple," while the tides in all 

 other seas " are comparatively complicated, but regular and explicable." However 

 tliis ma}^ be, specialists should direct tlieir attention to the disentanglement of the 

 variations in the sea-level from tidal action simple ; and our colonies, especially 

 tliose in the southern hemisphere, would be excellent fields for the gatheriug-in of 

 reliable observations. 



I am unwilling to leave the subject without tracing some of the consequences 

 that might be fairly considered to follow this assumed change of level in the 

 North-Atlantic basin. We can by it conceive the gradual working-up of the 

 warmed water from southern sources as the winter season approaches, including : — 

 the expansion of the Gulf-stream in the autumn months; the consequent welling- 

 np of a head of water in the enclosed and comparatively limited area northward of 

 Spitzbergen, Greenland, and the broken land westward of Smith Sound ; the 



