624 



Dr. W. B. Carpenter on the 



[June 13, 



stream and the Arctic current, — not between the Gulf-stream and the 

 ordinary Oceanic water, — that the prevalent notions respecting its special 

 heating-power are mainly founded. Thus Admiral Sir Alexander Milne, 

 proceeding in H.M.S. 'Nile' from Halifax to Bermuda in May 1861, 

 found the temperature 70° at the bow, when it was only 40° at the stern ; 

 thus showing a difference of 30° within the ship's length. When, on the 

 other hand, the temperature of the eastern edge of the Gulf- stream in the 

 earlier part of its course, and of the southern edge in the later part of its 

 course, is compared with the normal of the neighbouring portion of the 

 Atlantic, the difference is found to be comparatively slight, the one gra- 

 duating into the other. 



144. The average rate of two miles per hour, which the Gulf-stream 

 in the Narrows, is maintained to Lat. 30°; but it then begins to 



show a decided reduction, falling to 40 miles per day between 30° and 33° 

 N. Lat. When the Stream has passed Cape Hatteras, and its land side is 

 pressed on by the Arctic current, this compression seems to have the same 

 effect in increasing its velocity that limitation between banks would exert ; 

 for the rate of flow there rises again, sometimes exceeding four miles per 

 hour. At the same time the rate of the Stream at its outer edge is not 

 greater than from 10 to 20 miles per day. The direction of the Stream is 

 gradually changed by the trend of the coast-line, first from N. to N.E. by 

 N., then to N.E., and subsequently, after being subject to the influence of 

 the Arctic current, to E.N.E. Part of this Easterly deflection, how- 

 ever, is probably to be attributed to the greater easterly momentum which 

 this body of water brings with it from its southern source, in virtue of its 

 excess of rotary velocity ; as was first pointed out by Capt. Maury, whose view 

 on this point was adopted by Sir John Herschel. And, of course, the further 

 North the Stream advances, the more strongly will this excess show itself, 

 in giving to the movement of the Stream an Easterly direction. Conversely, 

 the Arctic Current coming Southwards will bring with it a smaller rotary 

 velocity than that of the parallel it reaches, and will thus have a Westerly 

 tendency, which will keep it close to the coast-line of the United States. 



145. Very early in its course, the Gulf-stream begins to show a division 

 into alternate bands of warmer and colder water ; and these become very 

 perceptible before it passes Charleston. The cause of this division appears 

 to lie in the contour of the bottom in the Florida Channel ; the elevations 

 of which, as already stated (§ 132), throw up the colder water of the deeper 

 stratum nearer to the surface. With the increase in the breadth of the 

 Stream as a whole, there is at the same time an increase in the distance 

 between the bands. Thus at Cape Hatteras, where the " cold wall" sepa- 

 rating the Gulf-stream from the Arctic Current is 30 miles from shore, 

 the first or axial band of the Gulf-stream has a breadth of 47 miles ; to 

 the east of this there is a cold band 25 miles broad ; and this is succeeded 

 by another warm band of 45 miles. These two warm bands, with the 

 intervening colder band, are considered by Prof. Bache as constituting the 



