414 OBSEEVATIONS ON THE CUERENTS. 



is some point where there is no movement. Making all possible allowance 

 for the decrease in velocity from 48*0 miles on the surface to O'O at the 

 bottom (and this must be done in an empirical manner, and may bo miMch 

 overrated) the mean velocity of the whole mass will not exceed 36-25 miles 

 per day. The sectional area of the Stream not exceeding 6"64 square miles, 

 it follows that there are not more than 240-7 cubic miles of water passing 

 per day over a given line in this part of its course. 



Its mean rate of progress, when passing Cape Hatteras, is given as 

 nearly the same as in the Narrows, 47-2 miles per day, though this is in 

 excess of the velocities given at intermediate points. The surface water 

 will take 13|^ days to pass from Cape Florida to Cape Hatteras, 630 miles 

 apart ; but if the whole mass maintains the same rate, it will not pas? 

 over under 17 days, and will be, at the annual mean, only 4-2° Fahrenheit 

 cooler (varying from 10° to 1-2°). Off New York, it will be 10° cooler 

 (varying from 17° in winter to 3-9° in August). Off Cape Hatteras the 

 breadth of the Stream may be 120 miles, therefore it has expanded to a 

 breadth of more than three times (3-3) its width at the Outfall, and its 

 whole mass will make a bed of water 366 feet thick. 



From this line to that of the section running S.E. of Nantucket, thp 

 distance is about 480 miles. On and near this section temperature sound- 

 ings were taken by the United States Coast Surveyors, Commander Craven 

 in 1854, Davis in 1845, and Bache in 1846, and their observations place 

 us in a difficulty ; for the warmer waters were not found to exist North- 

 ward of the parallel of 38° N. ; the " Cold Wall " showed itself to the 

 North of this, and then two less warm beds as far as 40° N. But the 

 observations for current motion show its Eastern progress much farther 

 than this, in fact up to 41° N. If we accept the lower estimate of its rate 

 made by the Meteorologial Office, it will take 16 days to move the whole 

 mass from Hatteras to Nantucket, or 33 days from the Outfall, though its 

 temperature has only reduced from 12° to 18° since it left the Gulf of 

 Florida. It is this rapid course, and consequent preservation of its original 

 warmth, that has always made it so remarkable. 



But while it has thus carried the Tropical heat so near to, and amidst 

 the Arctic cold, its volume must be spread over a very much wider space, 

 for its somewhat undefined breadth off Nantucket may be assumed at 

 300 miles, or seven times its original breadth ; and if its velocity through- 

 out were equal, it could only be 170 feet deep, but as its rate has some- 

 what diminished it may be taken as 200 feet ; but then its surface has 

 much cooled down, and the body of warm water cannot be assumed even 

 as high as this calculation makes it. 



The investigations in the Blake led Lieutenant Pillsbury to infer the 

 volume of warm water passing the Narrows in 1 hour to be 89,872,000,000 

 tons, almost exactly one-half of this flow being within 100 fathoms of the 

 surface. At the rate of 35 cubic feet of sea-water to the ton, this would 

 amount to close upon 350 cubic miles of water per day, a considerable 

 increase on the figures given above, but still insufficient to affect the 

 argument to any appreciable degree. 



(407.) This brings this wonderful Current down to the new phasa of its 

 character. Hitherto it has been a rapid heat-bearing stream, pressing on 



