68 THE LAST CRUISE OF THE CARNEGIE 



After the evening time-sight and dechnation-observation, we 

 noticed a change in the color of the sea. It lost its grayish-green 

 tint and became clear blue. The seawater thermograph had 

 shown great variations in temperature for several hours, and now 

 read 75° Fahrenheit. At noon it had been only 46°. We were 

 in the Gulf Stream. 



Whole volumes have been written about this "mighty river in 

 the ocean" first charted by Benjamin Franklin just prior to the 

 Revolutionary War. It had long been noticed that the time 

 consumed in a western passage from England to America was 

 considerably greater than for the return. But the Nantucket 

 sea-captains, who were all acquainted with this current, had con- 

 sistently been able to bring their heavy laden cargo-vessels to 

 Boston many days sooner than the crack English mail-packets. 



This state of affairs annoyed Franklin, who was then post- 

 master, and he determined to investigate the cause. He con- 

 ferred with the Nantucket whalers, and found that they were 

 well aware of a "stream, on the edges of which they fish, and 

 that if they do not find their game on one edge, they cross the 

 stream, and try the opposite edge." 



Franklin was not content with these reports, although the 

 fishermen were able to give him the geographical limits of the 

 current, in the neighborhood of New England. In his character- 

 istic manner he set out to investigate it scientifically. He says: 

 "A stranger may know when he is in the Gulf Stream by the warmth 

 of the water; the warmth of that water, which the stream forms, 

 being much greater than the warmth of the water on each side 

 of it. If the navigator is bound to the westward, he should cross 

 the stream, and get out of it as soon as possible; whereas, if you 

 get into the Gulf Stream, you will be retarded by it at the rate 



of sixty to seventy miles a day I have, in the course of 



my passages to and from America, made several experiments 

 with the thermometer on the warmth of the water within the 

 Gulf Stream; and of the difference at the edges." 



Franklin plotted the course and limits of the current, as he had 

 measured them, on the chart hanging on the walls of the post- 

 office. He advised all American shipping to use this knowledge 



