QQ THE PHYSICAL GEOGRAPHY OF THE SEA. 



for our coast in all weathers. And so viewing it, tlie doctor, 

 through political considerations, concealed his discovery for a while. 

 It was then not uncommon for vessels to be as much as 10° out 

 in their reckoning. He himself was 5°. The prize of £20,000, 

 which had been offered, and partly paid to Harrison, the chro- 

 nometer maker, for improving the means of finding longitude at 

 sea, was fresh in the minds of navigators. And here it was thought 

 a solution of the grand problem — for longitude at sea was a grand 

 problem — had been stumbled upon by chance ; for, on approach- 

 ing the coast, the current of warm water in the Gulf Stream, and 

 of cold water on this side of it, if tried with the thermometer, 

 would enable the mariner to judge with great certainty, and in the 

 worst of weather, as to his positioa. Jonathan Williams after- 

 ward, in speaking of the importance which the discovery of these 

 warm and cold currents would prove to navigation, pertinently 

 asked the question, " If these stripes of water had been distin- 

 guished by the colors of red, white, and blue, could they be more 

 distinctly discovered than they are by the constant use of the 

 thermometer ?" And he might have added, could they have mark- 

 ed the position of the ship more clearly ? 



104. When his work on Thermometrical Navigation appeared, 

 Commodore Truxton wrote to him: "Your publication will be 

 of use to navigation by rendering sea voyages secure far beyond 

 what even you yourself will immediately calculate, for I have 

 proved the utility of the thermometer very often since we sailed 

 together. 



" It will be found a most valuable instrument in the hands of 

 mariners, and particularly as to those who are unacquainted with 



astronomical observations ; these particularly stand in need 



of a simple method of ascertaining their approach to or distance 

 from the coast, especially in the winter season ; for it is then that 

 passages are often prolonged, and ships blown off the coast by 

 hard westerly winds, and vessels get into the Gulf Stream with- 

 out its being known ; on which account they are often hove to by 

 the captains' supposing themselves near the coast when they are 

 very far off (having been drifted by the currents). On the other 

 hand, ships are often cast on the coast by sailing in the eddy of 



