140 The National Geographic Magazine 



salt contained is raised by evaporation 

 above the average. 



Another important fact in connection 

 with the stream is its almost tropical 

 temperature, due to the fact that its 

 high velocity enables it to reach the 

 middle latitudes with very little loss of 

 heat. Upon entering its limits, the 

 temperature of the sea water frequently 

 shows a rise of io° and even 15 . It 

 was this fact that gave to the stream in 

 the later years of the eighteenth century 

 and the earlier 5'ears of the nineteenth 

 an importance in the minds of navi- 

 gators that it no longer possesses. In 

 those days the chronometer, invented 

 by Harrison in 1765, was still an ex- 

 periment. Instruments were crude and 

 nautical tables often at fault. The re- 

 sult was that the determination of the 

 longitude was largely a matter of guess- 

 work, a vessel after a voyage from the 

 channel to America often being out of 

 her reckoning by degrees instead of by 

 minutes. The idea, first suggested by 

 Benjamin Franklin, that the master of 

 a vessel, by observing the temperature 

 of the surface water, could tell the 

 moment of his entry into the Gulf 

 Stream, and could hence fix his position 

 to within a few miles, was hailed with 

 delight. The method was published in 

 1799 by Jonathan Williams in a work 

 lengthily entitled " Thermometrical 

 Navigation, being a series of experi- 

 ments and observations tending to prove 

 that by ascertaining the relative heat 

 of the sea water from time to time, the 

 passage of a ship through the Gulf 

 Stream, and from deep water into sound- 

 ings, may be discovered in time to avoid 

 danger." In this work he makes the 

 patriotic comparison of the Gulf Stream 

 to a streak of red, white, and blue painted 

 upon the surface of the sea for the 

 guidance of American navigators. 



The discovery of the stream is also 

 alleged to have exercised a curious ef- 

 fect upon the commerce of some of our 

 southern cities. In those days, when 



the only known sailing route was by way 

 of the trades, it was the custom for ves- 

 sels making the voyage from Europe 

 late in the year to winter and refit at 

 Charleston or Savannah before attempt- 

 ing to reach the more northern ports of 

 Boston and New York, the prevalence 

 of the northwesterly gales along the 

 coast during the winter season render- 

 ing the passage a trying one even to 

 the larger ships and with the better 

 navigation of the present time. The 

 southern cities thus became to a certain 

 degree half-way houses on the voyage, 

 greatly to the benefit of their trade. 

 With the aid of a thermometer, how- 

 ever, a vessel once making the stream 

 was enabled to remain in its midst and 

 to be thus borne along by the current 

 until the desired northing was made, 

 after which she headed up for port. 

 Thus the necessity for making Charles- 

 ton or Savannah was obviated, and the 

 advantage which they had hitherto en- 

 joyed as commercial centers was lost. 



From Hatteras the course of the stream 

 leaves the coast in an east-northeast 

 direction. It ceases to exist as a stream 

 current — that is, as a current which runs 

 independently of the winds — shortly 

 after crossing the 40th parallel, and 

 even previous to that, the current ob- 

 servations in the square bounded by 

 35°-4P° N., 65°-7o° W. (off the coast 

 from Hatteras to Sand3' Hook), show- 

 ing for the month of maximum fre- 

 quency (September) but 32 per cent of 

 the whole number of observations set- 

 ting northeast — i. <?. , only 7 per cent 

 more than 25 per cent, which would 

 be the number if there were no directive 

 influence whatever. In this latitude it 

 becomes part and parcel of the general 

 easterly drift which characterizes the 

 waters of the ocean north of 35 ° in a 

 manner quite analogous to the westerly 

 drift of the tropics and due to the same 

 cause, namely, the prevailing winds. In 

 this latitude, however, the latter show 

 none of the persistency of the trades. 



