TRANSACTIONS OP THE SECTIONS. 21 



here failed, the mean of the registered observations may be a little too low ; but the 

 obvious deduction nevertheless remains untouched, of the descent of a polar curient 

 within the tract of the Gulf-stream by the coasts of New England. 



The relations of the Polar current aiid Gulf- stream, as thus indicated by the analyses 

 of thirteen transatlantic passages generally, change, it should be observed, materially 

 •with the seasons of the year. Thus the descending Polar current, which appears so 

 prevalent within the western half of the belt of waters referred to in the discussion 

 of the whole of the voyages, is found to be of comparative small importance in the 

 summer and autumn passages, whilst the Gulf- stream is then the most predominant. 

 Hence the shifting of the upper margin of the Gulf-stream northward at these sea- 

 sons, as popularly understood, obtains very decided confirmation. 



In the results thus derived from the discussion of original observations on surface 

 temperature of the North Atlantic, there will be found a general agreement with the 

 conclusions of many other observers ; but these now communicated, it is presumed, 

 will be found of some importance as to the specific information yielded in respect of 

 the belt of waters referred to. The indications, too, of a variety of effects from the 

 meeting of contrary currents, are perhaps as conclusive as they are in some respects 

 remarkable ; for from the results now obtained, taken in connexion with a few 

 auxiliary facts, we may safely infer the following varieties of operation derived from 

 the meeting of the polar and tropical currents within the track discussed : — 



1. Strata Currents, consisting of a continuance of the respective currents after 

 meeting in or near their original direction, by the overlaying of the denser waters 

 from the North by the warm water of the Florida stream. Of this characteristic 

 we have the most striking evidence in the observations of the Coast Survey of the 

 United States, by intersections of the Gulf-stream. Thus in tracks across the stream 

 having a general surface temperature of 80° to 82°, a depression of 10° to 15° was 

 usually found at depths not exceeding 120 fathoms ; of 20° to 25° at depths short of 

 500 fathoms ; and in cases of 700 fathoms and upwards, a reduction sometimes of 

 about 40° below the surface temperature ! So that the existence of strata currents 

 in this region of research — the Gulf-stream flowing above and the polar current 

 below — seems to be unquestionable. 



2. Interlacing Cm-rents — where the polar and tropical currents on meeting seem to 

 run past each other in repeated alternations of comparatively small breadth, in the 

 manner of the fingers with the clasped hands — were strikingly shown in the rapid 

 and great changes of the surface temperature within the fifth decimate section ; and 

 there is reason to believe that in these interlacings the edges of the respective waters 

 flowed past each other with little intermingling, as if guided by walls in separate 

 channels. 



3. Deflected Currents— where currents on meeting from different but not exactly 

 opposite quarters, as, for instance, from the S.W. andN. — are partially or mutually 

 deflected into an easterly direction, so as to give rise to certain branches falling, as 

 to one, on the southern coasts of Europe, and, as to the other, on the Noiway and 

 Spitzbergen shores. This species of mutual action in dense streams of water may 

 find familiar illustration in places where the ebb-stream from a river falls into the 

 tide-stream of the coast — the former pushing away the other, and each for a time 

 pursuing a separate deflected course, with but little apparent intermingling. 



4. Passing Currents — where they run in parallel but opposite courses, and over 

 separate ground — as in the distinctive Gulf-stream, in its general body, and the inshore 

 polar current running within it over the St. George's and other American banks. Of 

 the distinctiveness of the inshore polar current. Dr. Scoresby adduced this very 

 striking evidence, — 1st, that in observations on the temperature at the surface and 

 bottom on the St. George's Bank made on one of his voyages, the surface tempera- 

 ture was, with trifling difference, maintained below : thus in latitude 40° 43', longi- 

 tude 68° 35', the surface and the bottom, in 35 fathoms water, were both (May 22) at 

 the temperature of 46° ; and nearer the shore, in 69° 39' W., when the surface was 

 at 47°, the bottom in 39 fathoms was at 45° ; and 2ndly, that the New England and 

 New York pilots remark, in regard to an inshore current guided by the direction of 

 the wind, that the current running south-westerly under a north-easterly gale is much 

 stronger than the contrary current urged by a south-westerly gale. 



In regard to the surface temperature and great currents of the Northern Ocean, 



