G4 THE PHYSICAL GEOGRAPHY OF THE SEA. 



York, and tliought the landfall by no means bad. Chronometers, 

 now so accurate, were then an experiment. The Nautical Ephem- 

 eris itself was faulty, and gave tables which involved errors of 

 thirty miles in the longitude. The instruments of navigation 

 erred by degrees quite as much as they now do by minutes ; for 

 the rude " cross staff" and " back staff," the " sea-ring" and " mar- 

 iner's bow," had not yet given place to the nicer sextant and cir- 

 cle of reflection of the present day. Instances are numerous of 

 vessels navigating the Atlantic in those times being 6°, 8°, and 

 even 10° of longitude out of their reckoning in as many days from 

 port. 



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

 Finding longitude rccrossiug the Gulf Stream almost daily for three 

 by the Gulf stream, ccnturlcs, it nevcr occurred to them to make use of 

 it as a means of giving 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 afforded by 

 the temperature of its waters and that of the sea betw^een 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 oft- 

 en erred in their reckoning. 



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

 Foiger's Chart, sulted as to a memorial which the Board of Customs 



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

 mouth packets were generally a fortnight longer to Boston than 

 common traders were from London to Providence, Ehode Island. 

 They therefore asked that the Falmouth packets might be sent to 

 Providence 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. Jle, however, consulted Captain Folger, a 

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

 man explained to the philosopher that the difference arose from the 

 circumstance that the Ehode Island captains were acquainted with 

 the Gulf 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 



