6 Historical Introduction 



One important consequence of these early thermometric measurements 

 was the discovery of pockets of cold water in the Gulf Stream. These 

 pockets were first observed on the noteworthy cruise of the packet Eliza, 

 en route from Halifax to England in April, 1810 (see Kohl, 1868), In the 

 middle of the warm water of the Gulf Stream a mass of water colder than 

 the surrounding water by about 10-15° Fahrenheit, and some 200 miles 

 in diameter, was discovered. The explanation offered at the time was that 

 these cold spots were due to the melting of icebergs entrapped by the Gulf 

 Stream. This occurrence suggests a phenomenon very much Hke the large 

 cold eddy reported in recent times by Iselin and FugHster (1948), but its 

 real nature and cause must remain in the realm of surmise. Another view, 

 much in accord with modern synoptic experience, was that held by John 

 Hamilton, who made serial air and water temperature measurements 

 during twenty-six voyages to and from Europe, and asserted that the 

 Gulf Stream was so unsteady and shifted its position so frequently that it 

 was impossible to define its Hmits. Both Humboldt (1814) and Sabine 

 (1825) were convinced that changes in the strength of the trades affected 

 the Gulf Stream, and Sabine even suggested the use of weather ships 

 which, he said, should observe the Florida Current and then sail quickly to 

 Europe with the news of how strongly it was flowing, so that weather 

 predictions could be made. 



In 1832 the results of an extensive compilation by James Rennell of data 

 from the British Admiralty Office were pubHshed posthumously, Rennell 

 distinguished clearly between 'drift currents', which are produced by the 

 direct stress of the wind, and what he called 'stream currents', which are 

 produced by a horizontal pressure gradient in the direction of flow. 

 Rennell, in accord with Franklin's earUer view, regarded the Gulf Stream 

 as a current of the second kind and decided from his investigation that : 

 (i) the breadth of the Stream changes from time to time ; (ii) the breadth 

 can vary as much as twofold even within so short a period as ten weeks; 

 (iii) the variations are not seasonal; (iv) the north side of the Stream is 

 more permanent than the south side ; (v) temperature alone does not prove 

 the existence of the Stream, for even warm countercurrents may exist ; and 

 (vi) cold-water inclusions occur within the body of the warm water. Also, 

 Rennell proposed a special nomenclature for various parts of the Gulf 

 Stream System. 



The work of Rennell was so authoritative and exhaustive at the time 

 that it must have seemed to his contemporaries that the major features of 

 the Gulf Stream had been deUneated and charted. Few seriously enter- 

 tained doubts that the Gulf Stream was a result of the downhill flow of 

 water piled up by the trade winds along the American coast and in the 

 Gulf of Mexico. 



