66 PHYSICAL GEOGRAPHY OF THE SEA, AND ITS METEOEOLOGY. 



182. Though navigators had heen in the habit of crossing and 

 Finding longitude reci'ossing the Grulf Stream almost daily for three 

 by the Gulf Stream, centimes, it nover occurred to them to make use of 

 it as a means of gi^'ing them their longitude, and of warning them 

 of their approach to the shores of this continent. Dr. Franklin 

 was the first to suggest this use of it. The contrast aiforded by 

 the temperature of its waters and that of the sea between the 

 Stream and the shores of America was striking. The dividing 

 line between the warm and the cool waters was sharp (§ 70) ; and 

 this dividing line, especially that on the western side of the stream, 

 seldom changed its position as much in longitude as mariners often 

 erred in their reckoning. 



183. When he was in London, in 1770, he happened to be con- 

 Foigers Chart, sultcd as to a memorial which the Board of Customs 



at Boston sent to the Lords of the Treasmy, stating that the Fal- 

 mouth packets were generally a fortnight longer to Boston than 

 common traders were from London to Providence, Khode Island. 

 They therefore asked that the Falmouth packets might be sent to 

 Pro^adence instead of to Boston. This appeared strange to the doc- 

 tor, for London was much farther than Falmouth, and from Fal- 

 mouth the routes were the same, and the difference should have 

 been the other way. He, however, consulted Captain Folger, a 

 Nantucket whaler, who chanced to be in London also ; the old fisher- 

 man explained to the philosopher that the difference arose fi'om the 

 circumstance that the Pthode Island captains were acquainted with 

 the G-ujf Stream, while those of the English packets were not. 

 The latter kept in it, and were set back sixty or seventy miles a 

 day, while the former avoided it altogether. He had been made 

 acquainted with it by the whales which were found on either side 

 of it, but never in it (§ 158). At the request of the doctor, he 

 there traced on a chart the course of this stream from the Straits 

 of Florida. The doctor had it engraved at Tower Hill, and sent 

 copies of it to the Falmouth captains, who paid no attention to it. 

 The course of the Gulf Stream as laid down by that fisherman 

 from his general recollection of it, has been retained and quoted 

 on the charts for navigation, we may say, until the present day. 

 But the investigations of which we are treating are beginning to 

 throw more light upon this subject ; they are giving us more cor- 

 rect knowledge in every respect -^dth regard to it, and to many 

 other new and striking features in the physical geography of the sea. 



184. No part of the world affords a more difficult or dangerous 



