§ 187, 188. GULF STREAIVI, CLIMATES, AND COMMERCE. 57 



use of these warm and cold currents would prove to navigation, 

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

 distinguished 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 

 marked the position of the ship more clearly ? 



187. When his work on Thermometrical Navigation appeared, 

 Commodore Truxton. Commodore Truxtou wrote to him: "Your pub- 

 lication will be of use to navigation by rendering sea voyages se- 

 cure far beyond what even you yourself will immediately calcu- 

 late, for I have proved the utility of the thermometer ver}^ often 

 since we sailed together. It will be found a most valuable in- 

 strument 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 ascertain- 

 ing 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 without its being known ; on which ac- 

 count they are often hove to by the captains' supposing them- 

 selves 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 the Stream, which causes 

 them to outrun their common reckoning. Every year produces 

 new proofs of these facts, and of the calamities incident thereto." 



188. Though Dr. Franklin's discovery was made in 1775, yet. 

 The discovery of the for political rcasous, it was not s^enerally made 



high temperature of ^ .^ . i^r^ri -r • -1 



the Gulf Stream foi- kuowu till 1790. Its immediate effect in naviara- 



lowedbyadeclinein . ^ ^ 



Southern commerce, tioii was to make the ports of the North as access- 

 ible in winter as in summer. What agency this circumstance 

 had in the decline of the direct trade of the South, which followed 

 this discovery, would be, at least to the political economist, a sub- 

 ject for much curious and interesting speculation. I have re- 

 ferred to the commercial tables of the time, and have compared 

 the trade of Charleston with that of the northern cities for several 

 years, both before and after the discovery of Dr. Franklin became 

 generally known to navigators. The comparison shows an im- 

 mediate decline in the Southern trade and a wonderful increase 

 in that of the North. But whether this discovery in navigation 



