THE GULF STBEAM. 403 



(392.) The Mean Surface Temperature of the Gulf Stream, in the early 

 part of its course may be ascertained from the vast and confused mass of 

 figures contained in Captain Maury's Thermal Charts. The temperatures 

 thus recorded, however, show large variations between themselves in the 

 same periods. This may arise from two causes — the one from the varia- 

 tion known to exist in the Stream itself, and which is frequently con- 

 siderable ; and the other from the imperfection of the thermometers used, 

 and this, as many of the observations appear to have been derived from 

 voyages made before standard thermometers were employed, may include 

 a considerable portion of the discrepancies which exist. Another and 

 very important addition to this branch of the subject, is the work of 

 Lieutenant Andrau, " Onderzoekingen met den Zeethermometer," pub- 

 lished by the Netherlands Eoyal Meteorological Institute, Utrecht, 1861. 



The following are the results of the calculations for the temperature of 

 the main strength of the Current from the Narrows of the Little Bahama 

 Bank to the meridian of Halifax. To the Eastward of this, or of long. 60°, 

 the temperature, especially in winter and spring, becomes rapidly lower 

 and very irregular, as will be presently alluded to, and therefore our 

 comparison will now be limited to this section, which comprises a 

 distance of about 1,200 miles, and which is traversed by the Stream in 

 from 25 to 35 days. 



Winter.— on Matanilla Reefs, 77-2° ; off Charleston, 75-9° ; off Cape Fear, 73-6° ; 

 off Cape Hatteras, 71-0° ; off the Capes of Virginia, 71-0° ; S.E. of New York, 70-5 ; 

 S.E. of Nantucket, 67-9° ; South of Halifax, 62-5°. It has thus cooled 14-7° F. 

 in its passage. 



Sin-ing.—liD. Florida Strait, 77*5° ; off Charleston, 76-5^ ; off Cape Fear, 74-7° ; 

 off Cape Hatteras, 72-0° ; off the Capes of Virginia, 72-0^ ; S.E. of New York, 70*5 ; 

 S.E. of Nantucket, 67*4° ; South of Halifax, 63 5^. In the latter part of its course 

 it is cooler ia the spring than its ratio to the earlier part, owing to the higher 

 velocity of the Arctic Current, which flows under and mixes with it. 



Summer.— Iji Florida Strait, 83-2° ; off Charleston, 82-4; off Cape Fear, 81-2° ; 

 off Cape Hatteras, 79-8° ; off the Chesapeake, 79-8' ; S.E. of New York, 79-2'; 

 S.E. of Nantucket, 80-0'' ; South of Nova Scotia, 77"9''. Here the water preserves 

 its heat without much dimuiution, being only 5-3° colder than when it leaves the 

 Gulf. 



Autumn.— In Florida Strait, 81-7° ; off Charleston, 81'6° ; off Cape Fear, 78-0° ; 

 off Cape Hatteras, 75-5'^ ; off the Chesapeake, 75-5^ ; off New York, 73-0° ; off 

 Nantucket, 71-5° ; South of Nova Scotia, 69-2°. 



Upon comparing these temperatures, which are carried so many miles 

 unimpaired by the Gulf Stream, with those of the inner Arctic Current 

 between the Stream and the shores of Virginia, New Jersey, New York, 

 &c., a surprising difference will be seen, especially in the spring months, 

 when the difference is at a mean 30°, and in other seasons from 15° to 23°. 

 This will be more fully entered into in the next section. 



(393.) It has been found that the temperature of the Stream varies in a 

 greater degree than could be accounted for by the climates it had passed 

 through, being sometimes warmer to the North, and cooler to the South, 

 of any particular position. This seems to be accounted for by the varia- 

 bility of the source of the Stream in the Gulf of Mexico and elsewhere, 

 which it would be very difficult to follow up to any specific determination. 



