THE GULF STEEAM. 405 



meridian of 20° W., from lat. 40° to 10° N., a distance six times as great, 

 the average change in the temperature of the sea is but 15°. 



(394.) The investigations carried out by the United States Survey 

 steamer Blake, have thrown some light on this subject. Commander 

 Bartlett, U.S.N., who was in charge between 1877 — 1884, found that the 

 average surface temperature in the axis of the Stream rarely exceeded 83° 

 in June and July. On one or two occasions the thermometer read as 

 high as 86°, and once 89° at high noon in a dead calm. The temperature 

 at 5 fathoms did not range above the average of 81i^°. 



In 1881, in the Stream off Charleston, at a depth of 350 fathoms, the 

 temperature was 50°, but in a hole of 500 fathoms it fell as low as 38°. 

 The general average temperature of the bottom of the Stream was 45°. 



In 1882, near Cape Hatteras, the temperature in deep water was found 

 to be the same as in the Gulf of Mexico, but farther Northward, where 

 the Stream spreads out, the depths of equal temperatures approached 

 nearer the surface. 



Lieutenant Pillsbury found that in the Narrows of Florida Strait 

 the temperature of the Stream varied slightly according to the moon's 

 declination. Here the highest average temperature is at the axis of the 

 Stream, but there are times during the month when the sides are warmer 

 than the axis was at some other recent time. Isolated observations are 

 of but very little value, for at the same place the variations are great, even 

 in an interval of a few days or perhaps hours. All that we can say 

 positively is that cold surface water comes from either a polar direction or 

 from a lower stratum, and the direction of its flow may be toward any 

 point of the compass. 



In the Atlantic, the inner edge of the Stream is not necessarily marked 

 by a change of temperature. An abrupt difference may be met at the 

 true edge of the current, and the cold water may be moving N.E. or tne 

 warm water may be flowing S.W. It is probable, however, that at about 

 the time of high declination, warm water off Cape Hatteras indicates a 

 N.E. current, and that at low declination the edge of the warm water has 

 a set in the opposite direction. 



In running lines of soundings from the coast as far as the 100- 

 fathoms line, at intervals, from Cape Hatteras to beyond George's Bank, it 

 has generally been noticed that in the vicinity of a depth from 40 to 80 

 fathoms, the temperature of the water suddenly changes, the colder being 

 always found on the land side. The tidal impulse being about normal to 

 the coast, and the Stream's course at right angles to it. Lieutenant Pills- 

 bury believes that to this we may look for the cause of the lesser thermo- 

 metrical variations, owing to the vibratory movement thus produced on 

 the ocean's surface. 



(395.) Warm and Gold Bands. — After leaving the Strait of Florida, the 

 Gulf Stream was found, in the early operations of its investigation in 

 1845-48, to consist of a series of alternate bands of cold and warm water, 

 a fact which was very surprising at the time, but the results of succeeding 

 explorations to some extent confirmed the former ones in this respect. 

 Between Cape Florida and New York the Stream was found to be divided 

 into several bands of higher and lower temperatures, of which the axis 



