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Weather Almanac for February 2011
BENJAMIN FRANKLIN: ALWAYS WEATHERWISE
Benjamin Franklin’s lofty place in world history stems primarily from his role as one of the Founding Fathers of the United States in shaping the American Revolution. Franklin was also a social innovator — he set up one of the first lending libraries in the Colonies — and inventor — with credit for the bifocal glasses, a heating stove, the first flexible catheter in America, the odometer and the lightning rod among his many inventions. We could call him a scientist, writer/publisher and philosopher as well since his portfolio contains years spend as each.
But I like to think of Benjamin Franklin as one of the first North American meteorologists. His observations of the atmosphere gave us important early insights into the nature of lightning, the shape and movement of extratropical storms, the causes of whirlwinds, and factors that affect climate. Indeed, the image of Franklin that probably jumps into many minds when they hear his name is that of an older man flying a kite during a thunderstorm. And while not all weather proverbs are true, Franklin passed many useful weather words of wisdom into the public through his annual almanacs and the voice of “Poor Richard.”
The Early Years
Franklin was born in Boston, Massachusetts on 17 January 1706, the tenth and youngest son of Puritan soap maker, Josiah Franklin and Abiah Folger. He was also the fifteenth child of Josiah, who had been previously married. Ben had only a few years of formal education, which ended at age ten. At twelve, he became apprenticed as a printer to his older brother James. Ben ran away to Philadelphia five years later and worked at several printshops before traveling to England where he worked for a while as a typesetter.
Returning to Philadelphia as a young man, Franklin set up his own printing house and began a newspaper titled The Pennsylvania Gazette in 1728. Under the pseudonym of Richard Saunders, or “Poor Richard,” he began publishing Poor Richard’s Almanac in 1732. It continued annual publication until 1758. Poor Richard’s proverbs became part of the American heritage, and many are still quoted today: “A penny saved is a penny earned” and “Time is money” being but two. The success of the almanacs made the frugal Franklin wealthy. The almanac sold about 10,000 copies each year. Adjusting for population increases that circulation would equate to nearly 3 million copies per annum today.
In the following years, Franklin created a reading and social discussion club, the Junto, which, upon its transformation led to the establishment of the subscription Library Company of Philadelphia in 1731. In 1743, Franklin founded the American Philosophical Society to encourage scientific men to discuss their discoveries and theories among like thinkers. By this time, he had already begun his enquiries into the nature of electricity or “electrical fluid” as it was then known.
The success of his publishing/printing house allowed Franklin to retire from the printing business in 1747 and still receive profits from the business for another 18 years. This gave him time to debate politics and to apply his inquiring mind into science and invention, both social and mechanical. Although Franklin made many deep marks on history in the 43 years following his “retirement,” I hereafter focus on his meteorological accomplishments and leave it to his biographers to fill in the rest.
Franklin and the Sky
For most Americans of his day, weather was a popular topic for conversation, but, to paraphrase one of Franklin’s more popular aphorisms, while many were otherwise, Franklin was weatherwise. He had within his nature an insatiable curiosity for the world around him and that included the weather. His personal journal was filled with entries on the weather. And although there were many American weather observers and chroniclers, Franklin was undoubtedly America’s first meteorological scientist.
We know his interest in weather and climate covered at least six decades of his long life. While others before him had been weather observers, few set out to explain weather phenomena as Franklin did. He was the first American storm chaser, when in 1755, he took off after a large whirlwind on horseback. Franklin also studied lightning, storm movement, whirlwinds and waterspouts, evaporational cooling and raindrop formation as well as correlated the Gulf Stream with European climates and an extensive summer “fog” in 1783 — likely the dust from large volcanic eruptions (Laki in Iceland and Asama in Japan)— on the cold winter that followed.
In one set of note written on his return voyage from London in 1726, he included basic weather and ocean observations. One notable phenomenon he observed during this voyage was a lunar rainbow. His entry for 30 August 1926 reports “This evening, the moon being near full, as she rose after eight o’clock, there appeared a rainbow in a western cloud, to windward of us. The first time I ever saw a rainbow in the night caused by the moon.”
Unlike today’s meteorologists who are well versed in mathematics, the current “language” of the science, Franklin refrained from the use of math in his scientific work, and was proud of the fact. In concluding his paper on whirlwinds, he wittedly noted “If my hypothesis is not the truth itself it is least as naked: For I have not, with some of our learned moderns, disguised my nonsense in Greek, clothed it in algebra, or adorned it with fluxions. You have it in puris naturalibus.” [I believe here he uses fluxions to mean the mathematical practice of adorning a letter with a symbol to denote a mathematical operation such as a differential.]
The “Eclipse Storm” and The Movement of Hurricanes
One of Franklin’s most groundbreaking observations of the weather came in the Autumn of 1943. The astronomical almanacs had forecast a lunar eclipse for October 1743, and Franklin intended to observe that eclipse the evening of 21 October (1 November by our current calendar), but was prevented from doing so by a storm that made “the Sky thick clouded, dark and rainy, so that neither Moon nor Stars could be seen.”
The disappointed Franklin was surprised later to read accounts of the eclipse in the New England newspapers. He wrote his brother John in Boston to confirm the information, and he told Benjamin that the stormy weather arrived there about an hour after the eclipse had ended. The prevailing weather theory of the day held that storms moved linearly forward with the general direction of the wind. Since Franklin had observed strong northeasterly winds with the onset of the storm, he believed that the storm had travelled from the northeast, the direction of Boston from Philadelphia, to him. Therefore, storm clouds over Boston should have obscured the eclipse unless the storm had already left Boston. But not only were Boston’s skies open for the lunar event, John had said that the storm arrived after the eclipse. “This puzzles me, because the storm began with us so soon as to prevent any observation; and being a northeast storm, I imagined it must have begun rather sooner in places farther to the north-eastward than it did in Philadelphia.”
From the information he later gathered from other newspapers and personal correspondences, Franklin deduced that such large, violent storms that persisted along the coast for several days moved from the southwest toward the northeast, even though their winds blew from the northeast quadrant. His conjecture stopped short of ascribing a rotating circulation to the storms that we now call cyclonic, but Franklin had correctly concluded from his analysis that storms do not necessarily travel from the same direction as the wind blows. However, he did believe that some storms, such as thunderstorms moved with the general wind field, as in fact they do.
Not only was his hypothesis groundbreaking, but Franklin’s method of analysis — building a large-scale picture from many concurrent observations — would become the basis for synoptic meteorology and the weather map.
Six years following those observations on storm movement, Franklin wrote Jared Eliot on 16 July 1747 and expanded on his thesis by applying it to the movement of hurricanes. “Of these I have had a very singular opinion for some years, viz: that, though the course of the wind is from northeast to southwest, yet the course of the storm is from southwest to northeast; the air is in violent motion in Virginia before it moves in Connecticut, and in Connecticut before it moves at Cape Sable, etc.” He later expanded on the thesis in a letter to Eliot written 13 February 1750.
He also described his thinking in a similar letter to Alexander Small of London in May 1760.
“That is to say, the air in Georgia, the farthest of our colonies to the South-West, begins to move South-Westerly before the air of Carolina, which is the next colony North-Eastward; the air of Carolina has the same motion before the air of Virginia, which lies still more North-Eastward; and so on North-Easterly through Pensylvania [sic], New-York, New England, &c. quite to Newfoundland.”
In this simple study, Franklin had begun with a single observation, which might have been dismissed as an oddity, and derived an explanation that was well ahead of the thinking of the day. He was beginning to see the continental migratory nature of storm systems we now take for granted. His hypothesis, though still incomplete, was a groundbreaking achievement about which, nearly two centuries later, Harvard Professor William Morris Davis would remark in the Journal of the Franklin Institute that “with this began the science of weather prediction.”
An expanded account of this part of Franklin’s story can be found in my article Eclipsed by Storm. The 1750 letter to Eliot can be found at the end of that article.
Electricity in the Sky
Franklin began his studies of electrical fluid in the laboratory and soon came to understand the basic nature of electricity. He was the first to realize the principal of the conservation of electrical charge and to label the two charge states as positive and negative, or plus and minus. Other now-common electrical terms that Franklin coined include battery, charge, conductor and condenser. Interestingly, Franklin and his fellow investigators conducted their experiments in the Pennsylvania Statehouse, a building we now know as Independence Hall. Franklin also worked in his lab at his home.
From the lab, he took his knowledge and enquiries outdoors. Several scientists had speculated that lightning was, in fact, electricity, but Franklin was among the first to prove the point.
In 1750, Franklin proposed an experiment to prove the hypothesis that lightning was in fact electricity: the now-famous, and very dangerous, kite experiment. There is debate whether or not this was a real experiment that he actually performed or whether he conceived it as a thought experiment. Despite American folklore, we have no proof he actually flew that kite although he and his son did mention doing so, though much after the fact. The popular Discover Channel show MythBusters showed that had the experiment unfolded as the legend holds, Franklin would likely have been killed when lightning struck the kite. (And how history may have been different!) Indeed, in Russia, Georg Wilhelm Richmann actually was electrocuted while performing a similar experiment in the summer of 1753.
Franklin's Experiment, June 1752 Published by Currier & Ives 1876
If Franklin did actually fly the kite in a thunderstorm in 1752, it is most likely that the spark from the key held on the kite string resulted from the electrical potential differential between the air and the ground (see Why Lightning Bolts Are Not Straight), and not a direct hit, which could have killed him. Just prior (a month) to the date that Franklin supposedly flew the kite experiment, Frenchman Thomas-Francois Dalibard erected a 40-foot (12 m)-tall iron rod that attracted electrical sparks from a thundercloud thus proving Franklin’s underlying hypothesis that lightning was a form of electrical discharge.
Franklin undoubtedly understood the dangers of his experiment. He well knew the power of lightning and the consequences of a direct strike on buildings. His writings offered alternate experiments for proving that lightning was electricity. Combining pure science knowledge with practical concerns, Benjamin soon developed the lightning rod. If one attached “upright Rods of Iron, made sharp as a Needle and gilt to prevent Rusting, and from the Foot of those Rods a Wire down the outside of the Building into the Ground,” he conjectured. “Would not these pointed Rods probably draw the Electrical Fire silently out of a Cloud before it came nigh enough to strike, and thereby secure us from that most sudden and terrible Mischief!”
The first lightning rods were installed on his home and soon thereafter on the Academy of Philadelphia (later the University of Pennsylvania) and the Pennsylvania State House (later Independence Hall). Thereafter, lightning rods began rising from rooftops across the Colonies and Europe. In recognition of the achievement, The Royal Society awarded Franklin the prestigious Copley Medal in 1753, the first living recipient from outside Britain. Three years later, he was elected as a Fellow of the Society, one of the few Eighteenth Century Americans to be so honored.
Franklin also proposed a device that began as an experiment in electricity and became a device that warned his household of thunderstorms. He wrote to his friend English merchant and naturalist Peter Collinson that he erected his iron lightning rod, “fixed to the top of my chimney and extending abut nine feet above it. From the foot of this rod a wire (the thickness of a goose-quill) came through a covered glass tube in the roof and down through the well of the staircase; the lower end connected with the iron spear of a pump. On the staircase opposite to my chamber door the wire was divided; the ends separated about six inches, a little bell on each end; and between the bells a little brass ball, suspended by a silk thread, to play between and strike the bells when clouds passed with electricity in them.”
What he had devised was a lightning potential detector, which reacted to the buildup of charge differential between the air and the tip of the grounded rod and, through the bells indicated the potential for lightning nearby. His wife Deborah was not as amused by the device as he, and years later when he was away in London, wrote to ask how to disarm it. Apparently, its ringing bells and flashes of light unnerved her.
From this set-up, Franklin found that “the clouds of a thundergust are most commonly in a negative state of electricity, but sometimes in a positive state.” He believed that for the most part in thunder strokes, “tis the earth that strikes into the clouds, and not the clouds that strike into the earth.” Although this phrasing reads a bit odd; I believe that he is saying that the lightning bolt most often initially begins from the ground connection point and moves into the cloud rather than moving from the cloud to the ground point. As we know now, that is the case with most lightning bolts. (see Why Lightning Bolts Are Not Straight)
Explaining the Waterspout and Other Whirlings
In his paper Physical and Meteorological Observations: Conjectures and Suppositions (believed to have been compiled in 1751), Franklin addressed the weather conditions which form large eddies or whirlings (whirlwinds) in the atmosphere. “Thus these eddies may be whirlwinds at land, waterspouts at sea.” He conjectured that these were formed by air ascending or descending that had attained a circular motion. The air within receded “from the middle of the circle by a centrifugal force, and leaving there a vacancy; if descending, greatest above, and lessening downwards; if ascending, greatest below, and lessening upwards; like a speaking trumpet standing its big end on the ground. When the air descends with violence in some places, it may rise with equal violence in others, and form both kinds of whirlwinds.”
He continued: “The air in its whirling motion receding every way from the center or axis of the trumpet, leaves there a vacuum; which cannot be filled through the sides, the whirling air, as an arch, preventing; it must then press in at the open ends. … The air entering, rises within, and carries up dust, leaves, and even heavier bodies that happen in its way, as the eddy, or whirl, passes over land. If it passes over water, the weight of the surrounding atmosphere forces up the water into the vacuity… A body of water so raised may be suddenly let fall, when the motion, etc. has not strength to support it, or the whirling arch is broken so as to let in the air; falling in the sea, it is harmless, unless ships happen under it. But if in the progressive motion of the whirl, it has moved from the sea, over the land, and there breaks, sudden, violent, and mischievous torrents are the consequences.”
In October 1752, Massachusetts physician John Perkins, who had read Franklin’s conjectures on the nature of waterspouts, questioned some aspects of it based upon first-hand accounts of mariners who had witnessed waterspouts. He had doubts as to whether “water in Bulk or even broken into Drops ever ascends into the Region of the Clouds… I cannot conceive a Force producible by the Rarifaction [sic] and condensations of our Atmosphear [sic] in the Circumstances of our Globe capable of carrying Water in large portions into the Region of the Clouds. Supposing it to be raised it would be too heavy to continue the ascent beyond a considerable Height, unless parted into Small Drops: And even then by its centrifugal Force from the Manner of Conveyance it would be flung out of the Circle and fall scatter’d like Rain.” In other words, he could not conceive of an ascent of water from the surface into the cloud, only the descent of water from it to the surface. He then asked “Whether a Violent Tornado of a Small Extent and other Sudden and Strong Gusts be not Winds from Above descending nearly perpendicular. And whether many that are call’d WhirlWinds at Sea are any other than these, and so might be call’d Air Spouts, if they were Objects of Sight.”
In February 1753, Franklin answered the Perkins letter, presenting a detailed, nearly 4000-word, description of his theories on the topic. First, he agreed that waters could not be drawn up into the air by a vacuum to a height greater than 30 feet. However, Franklin’s viewing of the diagrams drawn from firsthand accounts led him to believe they favored his hypothesis. (For a full account of Franklin’s answer, see Franklin Explains The Waterspout.)
Franklin felt a whirlwind and spout as being one and the same, save their location of occurrence. He is quite correct if he considers a whirlwind only as a dust devil rather than a tornado, which is of the same genus Vortex but a different species. I make this interpretation based on this later sentence in his reply: “Whirlwinds generally arise after Calms and great Heats: The same is observ’d of Water Spouts, which are therefore most frequent in the warm Latitudes.” If he had meant tornado rather than dust devil, he would surely have emphasized the presence of a thunderstorm when one formed.
He then remarked: “There may be Whirlwinds of both kinds [ascending (rising) and descending], but from the common observ’d Effects, I suspect the Rising one to be the most common; and that when the upper Air descends, tis perhaps in a greater Body, extending wider and without much whirling as in our Thunder Gusts. When Air descends in a Spout or Whirlwind, I should rather expect it would press the Roof of a House inwards, or force in the Tiles, Shingles or Thatch; force a Boat down into the Water, or a Piece of Timber into the Earth than that it would lift them up and carry them away.” [Is this perhaps the first recognition of a thunderstorm downburst? However, downbursts lack the twisting motion.]
In the discourse, Franklin understands that “the lower Region of Air is often more heated and so more rarified [having lower density], than the upper; consequently [it is] specifically lighter.” In the situation of the waterspout, “heated Air may be very moist, and yet the Moisture so equally diffus’d and rarified, as not to be visible, till colder Air mixes with it, when it condenses and becomes visible. Thus our Breath, invisible in Summer, becomes visible in Winter.”
He then sets out a situation where clear and calm daytime weather in the summer will greatly heat the surface of the land/sea “together with the lower Region of Air Contact with it, so that the said lower Air becomes specifically lighter than the superincumbent higher Region of the Atmosphere, in which the Clouds commonly float. … The Consequence of this should be, as I imagine that the heated lighter Air being press’d on all Sides must ascend, and the heavier descend; and as this Rising cannot be in all Parts or the whole Area of the Tract at once, for that would leave too extensive a Vacuum, the Rising will begin precisely in that Column that happens to be the lightest or most rarified; and the warm Air will flow horizontally from all Points to this Column, where the several Currents meeting and joining to rise, a Whirl is naturally formed…”
In this, Franklin describes the process of formation of thermals caused by the rising of warmer and thus lighter air from the surface and horizontal convergence at the surface. It hits close to our understanding of these vortices, whirls and spouts, except for assuming that the water/dust is raised solely by “vacuum” (pressure differential) forces rather than being carried aloft by the ascending winds within the rising thermals (moved by density differentials). But considering that Franklin lacked direct personal observation and measurements, he laid an excellent groundwork for later scientists to improve on.
Chasing A Whirlwind
In 1755, Franklin had the opportunity to observe first-hand a large whirlwind or dust devil, perhaps, some say, even a very weak tornado. As it passed, he gave chase on horseback, thus making him America’s first storm chaser. Franklin’s observations were recorded in a letter to Peter Collinson dated 25 August 1755. (The full letter is reproduced in my article: Benjamin Franklin: The First American Storm Chaser.)
He reported the whirlwind “appeared in the form of a sugar-loaf [a cone], spinning on its point, moving up the hill towards us, and enlarging as it came forward. When it passed by us, its smaller part near the ground, appeared no bigger than a common barrel, but widening upwards, it seemed, at 40 or 50 feet high [12.2-15.2 m], to be 20 or 30 feet [6.1-9.1 m] in diameter.”
Franklin, along with his son, gave chase. “I could plainly perceive that the current of air they were driven by, moved upwards in a spiral line. … The course of the general wind then blowing was along with us as we travelled, and the progressive motion of the whirlwind was in a direction nearly opposite, though it did not keep a strait line, nor was its progressive motion uniform, it making little sallies on either hand as it went, proceeding sometimes faster and sometimes slower, and seeming sometimes for a few seconds almost stationary, then starting forward pretty fast again.”
“When we rejoined the company, they were admiring the vast height of the leaves, now brought by the common wind, over our heads. These leaves accompanied us as we travelled, some falling now and then round about us, and some not reaching the ground till we had gone near three miles from the place where we first saw the whirlwind begin.”
Deforestation and Climate
Climate provided Franklin with another venue of enquiry. Europeans had long assumed that the climatic conditions of a region were determined mostly by its latitude and were surprised that the climate conditions were harsher and colder in the American colonies than in equivalent European latitudes. During Franklin’s time, the American climate, as exemplified by the East Coast, was undergoing a noticeable warming trend. (The Little Ice Age was slowly waning during this period from its depths to the warmer times of the 20th Century.)
In 1763, one of the first climate change conferences was held in the Colonies, and Franklin agreed with other scholars that the cause was human intervention, specifically deforestation of the land. They argued that clearing the land of its great dense forests for agriculture and settlements, allowed the surface to absorb and store more of the sun’s heat and this melted the winter snow cover more quickly. Franklin, however, believed many more years of observation were necessary before the change could be verified. (Sound familiar?)
In 1771, Franklin wrote Thomas Percival, an English physician and pioneer of public health, continuing a discussion they had had on the size and growth of raindrops and hail.
Franklin believed that few drops of rain or hailstones reach the earth with the same size as when they began their fall from the clouds. Each drop/stone must thus continue water “addition in its progress downwards.”
“This may be [done in] several ways: by the union of numbers in their course, so that what was at first only a descending mist, becomes a shower; or by each particle in its descent through air that contains a great quantity of dissolved water, striking against, attaching to itself, and carrying down with it, such particles of that dissolved water, as happen to be in its way; or attracting to itself such as do not lie directly in its course, by its different state with regard either to common or electric fire; or by all these causes united.”
In this paragraph, Franklin describes the process of accretion, also known as collision and coalescence, one of the three means we know for increasing drop/stone size during descent. (See Raindrops, So Many Raindrops).
In his concluding paragraph, he makes another interesting observation that was later verified by meteorologists: that rain may actually begin as ice or snow in the cloud which melts on descent.
“Now we know that the rain, even in our hottest days, comes from a very cold region. Its falling sometimes in the form of ice, shews this clearly; and perhaps even the rain is snow or ice when it first moves downwards, though thawed in falling.”
Volcanoes and Climate
As the climate warming in America and Europe continued through the Eighteenth and Nineteenth Centuries, there were periods of setbacks: abnormally cold seasons. One of these occurred during the summer and winter of 1783 across Europe and a large part of North America. Following a cool and foggy summer, the 1783-84 winter was severe.
At the time, Franklin, the American Ambassador to France, was living in Paris. Noting the lack of sunlight during the summer months of 1783, he wrote “when the effects of the sun’s rays to heat the earth in these northern regions should have been the greatest, there existed a constant fog over all Europe, and great part of North America. This fog was of a permanent nature; it was dry, and the rays of the sun seemed to have little effect towards dissipating it, as they easily do a moist fog, arising from water.”
The impact of the constant fog “caused the earth to absorb less heat,” he reasoned. “Hence the surface was early frozen. Hence the first snows remained on it unmelted, and received continual additions. Hence perhaps the winter of 1783–4, was more severe than any that happened for many years.”
Although he could not positively ascertain the cause of the dry fog, he speculated that it came from “the vast quantity of smoke, long continuing to issue during the summer” from the volcanoes erupting around Iceland.” Although Franklin suggested the offending volcano was Hekla, it was the Laki fissure in Iceland in 1783 that erupted, producing the largest volume of lava flows in historic times. The Asama volcano in Japan also had a major eruption in 1783 that threw large quantities of dust and ash into the atmosphere and likely had a greater impact on the seasons that year.
“It seems however worth the inquiry, whether other hard winters, recorded in history, were preceded by similar permanent and widely extended summer fogs,” Franklin continued. “Because, if found to be so, men might from such fogs conjecture the probability of a succeeding hard winter . . . and take such measures as are possible and practicable, to secure themselves… .”
A few decades after his death, another major volcanic eruption, Tambora, would affect the global weather conditions, particularly across parts of North American and Europe. Known by various names (“The Year Without A Summer,” “Eighteen Hundred and Froze to Death”), the infamous year of 1816 would have widespread impacts when the summer proved so cold that crop production suffered. We now know that major volcanic eruptions, such as Mt Pinatubo in 1991, can cause atmospheric cooling over large areas of the globe for as long as two years following the eruption. The dust and ash emitted from these eruptions produce a hazy atmosphere, the dry fog, that Franklin observed.
The Gulf Stream
Another of Franklin’s major scientific “discoveries” was the Gulf Stream of the North Atlantic. Actually, he did not discover the Gulf Stream, it was known for centuries. (Ponce de Leon described it in 1513 with the first chart published in 1665 by Athanasius Kircher.) But Franklin did extensively chart it and by publishing those charts made its presence known to mariners.
Franklin's Map of the Gulf Stream Location
On his crossing of the Atlantic in 1724, Franklin and his traveling companion used their time on board to run several experiments during the voyage. One was to regularly check the temperature of the ocean waters, and Franklin was amazed at the differences recorded along the way. When the ship was within certain waters, which he observed also looked different; the temperature was nearly 20 F degrees (11 C degrees) warmer than in other waters.
While in England, Franklin had heard discussions on why it took longer for a British packet ship to travel from Falmouth, England to New York than for the trip from London, England to Newport, Rhode Island, despite the latter being a longer journey. When Franklin asked the question of his cousin, whaler captain Timothy Folger, Folger’s response was that American merchant ships knew of a strong eastbound current in the North Atlantic that they routinely avoided. When the mail packets sailed into the current, they were fighting a current that flowed rather steadily at 3 miles per hour (5 km/h) against them. The sailing time thus depended on the route taken and whether, and for how long, they encountered the opposing current.
With the help of Folger and other experienced captains, Franklin produced a chart of the current’s location, which was published in England in 1770. It was largely ignored by British captains but not by the Americans and French. Using knowledge of the Gulf Stream, ships traversing the North Atlantic were able to cut as much as two weeks from the transit time.
Franklin hypothesized that the trade winds cause the Gulf Stream by driving warm waters into the Gulf of Mexico, from where they exit by way of the Florida Strait and proceed to form the current. Having measured the temperature of the ocean at various depths on his final Atlantic crossing some six decades after his first, Franklin rightly surmised that the Gulf Stream was like a warm river flowing through the Atlantic Ocean. He suggested that a thermometer could, therefore, be used as a navigation aid. By checking the water temperature, a ship could determine how close they were to the core of the stream, where they could get the greatest push eastward (or could direct them away from the hindering stream on a westward voyage).
Other Meteorological Works
The above outline the major accomplishments of Benjamin Franklin in the meteorological sciences. But it does not cover all. In his letters and “Meteorological Imaginations and Conjectures,” he tackled other topics as diverse as: why the cold season begins and ends later than the sun’s elevation in the sky would suggest (the solar offset of the seasons); how hailstones formed; and how fog dissipated. He looked into what happened to the sun’s heat after it is absorbed by the soil and moved to a considerable depth and thus was one of the first to recognize temperature profiles in the soil.
Some of his insights include the following statements:
“There seems to be a region higher in the air over all countries, where it is always winter, where frost exists continually, since, in the middle of summer on the surface of the earth, ice falls often from above in the form of hail.” (Meteorological Imaginations and Conjectures, 1789)
“How immensely cold must be the original particle of hail, which forms the center of the future hailstone, since it is capable of communicating sufficient cold, if I may so speak, to freeze all the mass of vapor condensed round it, and form a lump of perhaps six or eight ounces in weight !” (Meteorological Imaginations and Conjectures, 1789)
“When in Summer time the Sun is high, and long every Day above the Horizon, his Rays strike the Earth more directly and with longer Continuance than in Winter; hence the Surface is more heated, and to a greater Depth by the Effect of those Rays.” (Meteorological Imaginations and Conjectures, 1789)
“Therefore the lakes north-west of us [in Pennsylvania], as the are not so much frozen nor so apt to freeze as the earth, rather moderate than increase the coldness of our winter winds. (Physical and Meteorological Observations, Conjectures, and Suppositions, 1754)
“The air in sultry weather, though not cloudy, has a kind of haziness in it, which makes objects at a distance appear dull and indistinct. This haziness is occasioned by the great quantity of moisture equally diffused in that air. When, by the cold wind blowing down among it, it is condensed into clouds, and falls in rain, the air becomes purer and clearer.” (Physical and Meteorological Observations, Conjectures, and Suppositions, 1754)
“Would not the earth grow much hotter under the summer sun, if a constant evaporation from its surface, greater as the sun shines stronger, did not, by tending to cool it, balance, in some degree, the warmer effects of the sun’s rays?” (“Cooling by Evaporation” in letter to John Lining, 1758)
“If two gun barrels electrified will strike at two inches' distance, and make a loud snap, to what a great distance may 10,000 acres of electrified cloud strike and give its fire, and how loud must be that crack?” (letter to Peter Collinson, 1750, printed as “Opinions and Conjectures” in Gentleman’s Magazine May 1750)
The Final Tally
Although Benjamin Franklin had only a few years of formal education, he endeavored to learn as much about the world around him as was possible and encouraged others to do so. He began the Academy and College of Philadelphia, the foundation of what would become the University of Pennsylvania, and formed the American Philosophical Society, both in 1743.
Franklin was recognized during his lifetime for some of his scientific achievements. In 1753, he received honorary degrees from Harvard and Yale. He was awarded the Copley Medal in 1753 and elected Fellow of the Royal Society in 1756. In 1759, Franklin was conferred with an honorary Doctor of Laws degree from the University of St Andrews, Scotland. In 1762, Oxford University also bestowed upon Franklin an honorary doctorate for his scientific accomplishments. Thereafter, he was often referred to as “Doctor Franklin.”
And, along the way, he helped write and signed both the Declaration of Independence and the US Constitution.
Asked to describe Benjamin Franklin’s contributions to meteorology, Professor Cleveland Abbe, himself a pioneer of American meteorology, remarked that he must add to the laurel that crowns Franklin another leaf “as the pioneer of the rational long-range forecasters, and of the physical meteorologists who will, undoubtedly, in the future develop this difficult subject.”
Learn More From These Relevant Books
The Field Guide to Natural Phenomena:
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