Benjamin Franklin's perspicacity never fails to amaze. In few places is his mental acuity more evident than his letters of correspondence, wherein Franklin frequently ruminated on topics scientific, technical and philosophical. What follows is an excerpt from one such letter, originally addressed to a scientific colleague in France, in which Franklin describes the process by which he came to produce the world's first map of the Gulf Stream.
It's worth pointing out that the Gulf Stream had been discovered long before Franklin set about creating the map; seafarers had known of the swift current's propulsive and impeding qualities for hundreds of years. But not before Franklin's map — first published in 1770 — had the Stream's location and effects been so widely known and accounted for. "If this one letter had been all that survived of Franklin's correspondence, he would have been remembered as a scientist of note and an individual with a remarkable span of knowledge on many subjects," note the curators of NOAA's Central Library. "As it is, this is one more example of why he is remembered as one of the greatest American intellects."
'Sundry circumstances relating to the Gulph Stream'
Vessels are sometimes retarded, and sometimes forwarded in their voyages, by currents at sea, which are often not perceived. About the year 1769 or 70, there was an application made by the board of customs at Boston, to the lords of the treasury in London, complaining that the packets between Falmouth and New York, were generally a fortnight longer in their passages, than merchant ships from London to Rhode-Island, and proposing that for the future they should be ordered to Rhode-Island instead of New-York. Being then concerned in the management of the American post office, I happened to be consulted on the occasion; and it appearing strange to me that there should be such a difference between two places scarce a day's run asunder, especially when the merchant ships are generally deeper laden, and more weakly manned than the packets, and had from London the whole length of the river and channel to run before they left the land of England, while the packets had only to go from Falmouth, I could not but think the fact misunderstood or misrepresented.
There happened then to be in London, a Nantucket sea-captain of my acquaintance, to whom I communicated the affair. He told me he believed the fact might be true; but the difference was owing to this, that the Rhode-Island captains were acquainted with the gulf stream, which those of the English packets were not. We are well acquainted with that stream, says he, because in our pursuit of whales, which keep near the sides of it, but are not to be met with in it, we run down along the sides, and frequently cross it to change our side: and in crossing it have sometimes met and spoke with those packets, who were in the middle of it, and stemming it. We have informed them that stemming a current, that was against them to the value of three miles an hour; and advised them to cross it and get out of it; but they were too wise to be counselled [counseled] by simple American fishermen.
When the winds are but light, he added, they are carried back by the current more than they are forwarded by the wind: and if the wind be good, the subtraction of 70 miles a day from their course is of some importance. I then observed that it was a pity no notice was taken of this current upon the charts, and requested him to mark it out for me which he readily complied with, adding directions for avoiding it in sailing from Europe to North-America. I procured it to be engraved by order from the general post office, on the old chart of the Atlantic, at Mount and Page's, Tower-hill, and copies were sent down to Falmouth for the captains of the packets, who slighted it however; but it is since printed in France, of which edition I hereto annex a copy.