The Citizen Scientist

Shawn Carlson, founder and Executive Director of the Society for Amateur Scientists, knows more about Benjamin Franklin, America's most distinguished amateur scientist, than anyone I know. He knows all about Franklin's electrical experiments and the stove he invented. He can tell you about Franklin's findings regarding the climatic impacts of the Laki volcanic eruption in Iceland in 1783-4. Shawn knows much more about Franklin's other scientific exploits, including his original research involving the flow and temperature of the Gulf Stream.

This was on my mind while reading Walter Isaacson's "Benjamin Franklin: An American Life." While this is a well written biography, it's emphasis is less on Franklin's science than the various other aspects of his complex life. So Shawn's knowledge of Franklin's science motivated me to explore the web for more information about one of the most famous amateur scientists in history.

In 1513 Ponce de Leon had reported on what became known as the Gulf Stream. Many others also reported its existence, and it was long known to fishermen. However, it was Franklin who first quantified it by measuring its temperature and appearance. He even published the first known map of the Gulf Stream.

Amateur scientists will be fascinated by this letter, which is a hallmark of maritime science and engineering. In the hope that a sample of this letter will lead amateur scientists to read the entire manuscript, reprinted here is the portion of Franklin's letter that addresses the Gulf Stream:

A Letter from Dr. Benjamin Franklin, to Mr. Alphonsus le Roy, member of several academies, at Paris. Containing sundry Maritime Observations.

Read Dec. your learned writings on the navigation of the ancients, which contain a great deal of curious information; and your very ingenious contrivances for improving the modern sails (voilure) of which I saw with great pleasure a successful trial on the River Seine have induced me to submit to your consideration and judgment, some thoughts I have had on the latter subject. ...

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.

This stream is probably generated by the great accumulation of water on the eastern coast of America between the tropics, by the trade winds which constantly blow there. It is known that a large piece of water ten miles broad and generally only three feet deep, has by a strong wind had its waters driven to one side and sustained so as to become six feet deep, while the windward side was laid dry. This may give some idea of the quantity heaped up on the American coast, and the reason of its running down in a strong current through the islands into the Bay of Mexico, and from thence issuing through the gulph [gulf] of Florida, and proceeding along the coast to the banks of Newfoundland, where it turns off towards and runs down through the western islands.

Having since crossed this stream several times in passing between America and Europe, I have been attentive to sundry circumstances relating to it, by which to know when one is in it; and besides the gulph [gulf] weed with which it is interspersed, I find that it is always warmer than the sea on each side of it, and that it does not sparkle in the night: I annex hereto the observations made with the thermometer in two voyages, and possibly may add a third. It will appear from them, that the thermometer may be an useful instrument to a navigator, since currents coming from the northward into southern seas, will probably be found colder than the water of those seas, as the currents from southern seas into northern are found warmer.

And it is not to be wondered that so vast a body of deep warm water, several leagues wide, coming from between the tropics and issuing out of the gulph [gulf] into the northern seas, should retain its warmth longer than the twenty or thirty days required to its passing the banks of Newfoundland. The quantity is too great, and it is too deep to be suddenly cooled by passing under a cooler air.

The air immediately over it, however, may receive so much warmth from it as to be rarified and rise, being rendered lighter than the air on each side of the stream; hence those airs must flow in to supply the place of the rising warm air, and meeting with each other, form those tornados and waterspouts frequently met with, and seen near and over the stream; and as the vapour [vapor] from a cup of tea in a warm room, and the breath of an animal in the same room, are hardly visible, but become sensible immediately when out in the cold air, so the vapour [vapor] from the gulph [gulf] stream, in warm latitudes is scarcely visible, but when it comes into the cool air from Newfoundland, it is condensed into the fogs, for which those parts are so remarkable.

The power of wind to raise water above its common level in the sea, is known to us in America, by the high tides occasioned in all our sea-ports when a strong northeaster blows against the gulph [gulf] stream.

The conclusion from these remarks is, that a vessel from Europe to North-America may shorten her passage by avoiding to stem the stream in which the thermometer will be very useful; and a vessel from America to Europe may do the same by the same means of keeping in it. It may have often happened accidentally, that voyages have been shortened by these circumstances. It is well to have the command of them.

But may there not be another cause, independent of winds and currents, why passages are generally shorter from America to Europe than from Europe to America. This question I formerly considered in the following short paper.

"Suppose a ship to make a voyage eastward from a place in lat. 40° north, to a place in lat. 50° north, distance in longitude 75 degrees.

" In sailing from 40 to 50, she goes from a place where a degree of longitude is about eight miles greater than the place she is going to. A degree is equal to four minutes of time; consequently the ship in the harbour [harbor] she leaves, partaking of the diurnal motion of the earth, moves two miles in a minute faster, than when in the port she is going to; which is 120 miles in an hour.

"This motion in a ship and cargo is of great force; and if she could be lifted up suddenly from the harbour [harbor] in which she lay quiet, and set down instantly in the latitude of the port she was bound to, though in a calm, that force contained in her would make her run a great way at a prodigious rate. This force must be lost gradually in her voyage, by gradual impulse against the water, and probably thence shorten the voyage. Query, In returning does the contrary happen, and is her voyage thereby retarded and lengthened ?"*

*Since this paper was read at the Society, an ingenious member, Mr. Patterson, has convinced the writer that the returning voyage would not, from this cause, be retarded.