Population studies
Franklin had a major influence on the emerging science of demography, or population studies. Thomas Malthus is famous for his rule of population growth and credited Franklin for discovering it. Kammen (1990) and Drake (2011) say Franklin's "Observations on the Increase of Mankind" (1755) stands alongside Ezra Stiles' "Discourse on Christian Union" (1760) as the leading works of eighteenth century Anglo-American demography; Drake credits Franklin's "wide readership and prophetic insight."
In the 1730s and 1740s, Franklin began taking notes on population growth, finding that the American population had the fastest growth rates on earth. Emphasizing that population growth depended on food supplies—a line of thought later developed by Thomas Malthus—Franklin emphasized the abundance of food and available farmland in America. He calculated that America's population was doubling every twenty years and would surpass that of England in a century. In 1751, he drafted "Observations concerning the Increase of Mankind, Peopling of Countries, &c." Four years later, it was anonymously printed in Boston, and it was quickly reproduced in Britain, where it influenced the economists Adam Smith and later Thomas Malthus. Franklin's predictions alarmed British leaders who did not want to be surpassed by the colonies, so they became more willing to impose restrictions on the colonial economy.
Franklin was also a pioneer in the study of slave demography, as shown in his 1755 essay.
Atlantic Ocean currents
As deputy postmaster, Franklin became interested in the North Atlantic Ocean circulation patterns. While in England in 1768, he heard a complaint from the Colonial Board of Customs: Why did it take British packet ships carrying mail several weeks longer to reach New York than it took an average merchant ship to reach Newport, Rhode Island? The merchantmen had a longer and more complex voyage because they left from London, while the packets left from Falmouth in Cornwall.
Franklin put the question to his cousin Timothy Folger, a Nantucket whaler captain, who told him that merchant ships routinely avoided a strong eastbound mid-ocean current. The mail packet captains sailed dead into it, thus fighting an adverse current of 3 miles per hour (5 km/h). Franklin worked with Folger and other experienced ship captains, learning enough to chart the current and name it the Gulf Stream, by which it is still known today.
Franklin published his Gulf Stream chart in 1770 in England, where it was completely ignored. Subsequent versions were printed in France in 1778 and the U.S. in 1786. The British edition of the chart, which was the original, was so thoroughly ignored that everyone assumed it was lost forever until Phil Richardson, a Woods Hole Oceanographer and Gulf Stream expert, discovered it in Bibliothèque Nationale in Paris in 1980. This find received front page coverage in the New York Times.
It took many years for British sea captains to adopt Franklin's advice on navigating the current; once they did, they were able to trim two weeks from their sailing time. In 1853, the oceanographer and cartographer Matthew Fontaine Maury noted that Franklin only charted and codified the Gulf Stream, he did not discover it:
Though it was Dr. Franklin and Captain Tim Folger, who first turned the Gulf Stream to nautical account, the discovery that there was a Gulf Stream cannot be said to belong to either of them, for its existence was known to Peter Martyr d'Anghiera, and to Sir Humphrey Gilbert, in the 16th century.
Electricity
His discoveries resulted from his investigations of electricity. Franklin proposed that "vitreous" and "resinous" electricity were not different types of "electrical fluid" (as electricity was called then), but the same electrical fluid under different pressures. He was the first to label them as positive and negative respectively, and he was the first to discover the principle of conservation of charge.
In 1750 he published a proposal for an experiment to prove that lightning is electricity by flying a kite in a storm that appeared capable of becoming a lightning storm. On May 10, 1752, Thomas-François Dalibard of France conducted Franklin's experiment using a 40-foot (12 m)-tall iron rod instead of a kite, and he extracted electrical sparks from a cloud. On June 15 Franklin may possibly have conducted his famous kite experiment in Philadelphia, successfully extracting sparks from a cloud. Franklin's experiment was not written up with credit until Joseph Priestley's 1767 History and Present Status of Electricity; the evidence shows that Franklin was insulated (not in a conducting path, where he would have been in danger of electrocution). Others, such as Prof. Georg Wilhelm Richmann were indeed electrocuted during the months following Franklin's experiment.
In his writings, Franklin indicates that he was aware of the dangers and offered alternative ways to demonstrate that lightning was electrical, as shown by his use of the concept of electrical ground. If Franklin did perform this experiment, he may not have done it in the way that is often described—flying the kite and waiting to be struck by lightning—as it would have been dangerous. Instead he used the kite to collect some electric charge from a storm cloud, which implied that lightning was electrical. On October 19 in a letter to England with directions for repeating the experiment, Franklin wrote:
When rain has wet the kite twine so that it can conduct the electric fire freely, you will find it streams out plentifully from the key at the approach of your knuckle, and with this key a phial, or Leiden jar, may be charged: and from electric fire thus obtained spirits may be kindled, and all other electric experiments [may be] performed which are usually done by the help of a rubber glass globe or tube; and therefore the sameness of the electrical matter with that of lightening completely demonstrated.
Franklin's electrical experiments led to his invention of the lightning rod. He noted that conductors with a sharp rather than a smooth point could discharge silently, and at a far greater distance. He surmised that this could help protect buildings from lightning by attaching "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;...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!" Following a series of experiments on Franklin's own house, lightning rods were installed on the Academy of Philadelphia (later the University of Pennsylvania) and the Pennsylvania State House (later Independence Hall) in 1752.
In recognition of his work with electricity, Franklin received the Royal Society's Copley Medal in 1753 and in 1756 he became one of the few 18th-century Americans elected as a Fellow of the Society. The cgs unit of electric charge has been named after him: one franklin (Fr) is equal to one statcoulomb.
Wave theory of light
Franklin was, along with his contemporary Leonhard Euler, the only major scientist who supported Christiaan Huygens' wave theory of light, which was basically ignored by the rest of the scientific community. In the 18th century Newton's corpuscular theory was held to be true; only after Young's famous slit experiment (1803) were most scientists persuaded to believe Huygens' theory.
Meteorology
On October 21, 1743, according to popular myth, a storm moving from the southwest denied Franklin the opportunity of witnessing a lunar eclipse. Franklin was said to have noted that the prevailing winds were actually from the northeast, contrary to what he had expected. In correspondence with his brother, Franklin learned that the same storm had not reached Boston until after the eclipse, despite the fact that Boston is to the northeast of Philadelphia. He deduced that storms do not always travel in the direction of the prevailing wind, a concept that greatly influenced meteorology.
After the Icelandic volcanic eruption of Laki in 1783, and the subsequent harsh European winter of 1784, Franklin made observations connecting the causal nature of these two separate events. He wrote about them in a lecture series.
Traction kiting
Though Benjamin Franklin has been most noted kite-wise with his lightning experiments, he has also been noted by many for his using kites to pull humans and ships across waterways. The George Pocock in the book A TREATISE on The Aeropleustic Art, or Navigation in the Air, by means of Kites, or Buoyant Sails noted being inspired by Benjamin Franklin's traction of his body by kite power across a waterway. In his later years he suggested using the technique for pulling ships.
Concept of cooling
Franklin noted a principle of refrigeration by observing that on a very hot day, he stayed cooler in a wet shirt in a breeze than he did in a dry one. To understand this phenomenon more clearly Franklin conducted experiments. In 1758 on a warm day in Cambridge, England, Franklin and fellow scientist John Hadley experimented by continually wetting the ball of a mercury thermometer with ether and using bellows to evaporate the ether. With each subsequent evaporation, the thermometer read a lower temperature, eventually reaching 7 °F (−14 °C). Another thermometer showed that the room temperature was constant at 65 °F (18 °C). In his letter Cooling by Evaporation, Franklin noted that, "One may see the possibility of freezing a man to death on a warm summer’s day."
Temperature's effect on electrical conductivity
According to Michael Faraday, Franklin's experiments on the non-conduction of ice are worth mentioning although the law of the general effect of liquefaction on electrolytes is not attributed to Franklin. However, as reported in 1836 by Prof. A. D. Bache of the University of Pennsylvania, the law of the effect of heat on the conduction of bodies otherwise non-conductors, for example, glass, could be attributed to Franklin. Franklin writes, "...A certain quantity of heat will make some bodies good conductors, that will not otherwise conduct..." and again, "...And water, though naturally a good conductor, will not conduct well when frozen into ice."
Oceanography findings
An aging Franklin accumulated all his oceanographic findings in Maritime Observations, published by the Philosophical Society's transactions in 1786. It contained ideas for sea anchors, catamaran hulls, watertight compartments, shipboard lightning rods and a soup bowl designed to stay stable in stormy weather.
Franklin had a major influence on the emerging science of demography, or population studies. Thomas Malthus is famous for his rule of population growth and credited Franklin for discovering it. Kammen (1990) and Drake (2011) say Franklin's "Observations on the Increase of Mankind" (1755) stands alongside Ezra Stiles' "Discourse on Christian Union" (1760) as the leading works of eighteenth century Anglo-American demography; Drake credits Franklin's "wide readership and prophetic insight."
In the 1730s and 1740s, Franklin began taking notes on population growth, finding that the American population had the fastest growth rates on earth. Emphasizing that population growth depended on food supplies—a line of thought later developed by Thomas Malthus—Franklin emphasized the abundance of food and available farmland in America. He calculated that America's population was doubling every twenty years and would surpass that of England in a century. In 1751, he drafted "Observations concerning the Increase of Mankind, Peopling of Countries, &c." Four years later, it was anonymously printed in Boston, and it was quickly reproduced in Britain, where it influenced the economists Adam Smith and later Thomas Malthus. Franklin's predictions alarmed British leaders who did not want to be surpassed by the colonies, so they became more willing to impose restrictions on the colonial economy.
Franklin was also a pioneer in the study of slave demography, as shown in his 1755 essay.
Atlantic Ocean currents
As deputy postmaster, Franklin became interested in the North Atlantic Ocean circulation patterns. While in England in 1768, he heard a complaint from the Colonial Board of Customs: Why did it take British packet ships carrying mail several weeks longer to reach New York than it took an average merchant ship to reach Newport, Rhode Island? The merchantmen had a longer and more complex voyage because they left from London, while the packets left from Falmouth in Cornwall.
Franklin put the question to his cousin Timothy Folger, a Nantucket whaler captain, who told him that merchant ships routinely avoided a strong eastbound mid-ocean current. The mail packet captains sailed dead into it, thus fighting an adverse current of 3 miles per hour (5 km/h). Franklin worked with Folger and other experienced ship captains, learning enough to chart the current and name it the Gulf Stream, by which it is still known today.
Franklin published his Gulf Stream chart in 1770 in England, where it was completely ignored. Subsequent versions were printed in France in 1778 and the U.S. in 1786. The British edition of the chart, which was the original, was so thoroughly ignored that everyone assumed it was lost forever until Phil Richardson, a Woods Hole Oceanographer and Gulf Stream expert, discovered it in Bibliothèque Nationale in Paris in 1980. This find received front page coverage in the New York Times.
It took many years for British sea captains to adopt Franklin's advice on navigating the current; once they did, they were able to trim two weeks from their sailing time. In 1853, the oceanographer and cartographer Matthew Fontaine Maury noted that Franklin only charted and codified the Gulf Stream, he did not discover it:
Though it was Dr. Franklin and Captain Tim Folger, who first turned the Gulf Stream to nautical account, the discovery that there was a Gulf Stream cannot be said to belong to either of them, for its existence was known to Peter Martyr d'Anghiera, and to Sir Humphrey Gilbert, in the 16th century.
Electricity
His discoveries resulted from his investigations of electricity. Franklin proposed that "vitreous" and "resinous" electricity were not different types of "electrical fluid" (as electricity was called then), but the same electrical fluid under different pressures. He was the first to label them as positive and negative respectively, and he was the first to discover the principle of conservation of charge.
In 1750 he published a proposal for an experiment to prove that lightning is electricity by flying a kite in a storm that appeared capable of becoming a lightning storm. On May 10, 1752, Thomas-François Dalibard of France conducted Franklin's experiment using a 40-foot (12 m)-tall iron rod instead of a kite, and he extracted electrical sparks from a cloud. On June 15 Franklin may possibly have conducted his famous kite experiment in Philadelphia, successfully extracting sparks from a cloud. Franklin's experiment was not written up with credit until Joseph Priestley's 1767 History and Present Status of Electricity; the evidence shows that Franklin was insulated (not in a conducting path, where he would have been in danger of electrocution). Others, such as Prof. Georg Wilhelm Richmann were indeed electrocuted during the months following Franklin's experiment.
In his writings, Franklin indicates that he was aware of the dangers and offered alternative ways to demonstrate that lightning was electrical, as shown by his use of the concept of electrical ground. If Franklin did perform this experiment, he may not have done it in the way that is often described—flying the kite and waiting to be struck by lightning—as it would have been dangerous. Instead he used the kite to collect some electric charge from a storm cloud, which implied that lightning was electrical. On October 19 in a letter to England with directions for repeating the experiment, Franklin wrote:
When rain has wet the kite twine so that it can conduct the electric fire freely, you will find it streams out plentifully from the key at the approach of your knuckle, and with this key a phial, or Leiden jar, may be charged: and from electric fire thus obtained spirits may be kindled, and all other electric experiments [may be] performed which are usually done by the help of a rubber glass globe or tube; and therefore the sameness of the electrical matter with that of lightening completely demonstrated.
Franklin's electrical experiments led to his invention of the lightning rod. He noted that conductors with a sharp rather than a smooth point could discharge silently, and at a far greater distance. He surmised that this could help protect buildings from lightning by attaching "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;...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!" Following a series of experiments on Franklin's own house, lightning rods were installed on the Academy of Philadelphia (later the University of Pennsylvania) and the Pennsylvania State House (later Independence Hall) in 1752.
In recognition of his work with electricity, Franklin received the Royal Society's Copley Medal in 1753 and in 1756 he became one of the few 18th-century Americans elected as a Fellow of the Society. The cgs unit of electric charge has been named after him: one franklin (Fr) is equal to one statcoulomb.
Wave theory of light
Franklin was, along with his contemporary Leonhard Euler, the only major scientist who supported Christiaan Huygens' wave theory of light, which was basically ignored by the rest of the scientific community. In the 18th century Newton's corpuscular theory was held to be true; only after Young's famous slit experiment (1803) were most scientists persuaded to believe Huygens' theory.
Meteorology
On October 21, 1743, according to popular myth, a storm moving from the southwest denied Franklin the opportunity of witnessing a lunar eclipse. Franklin was said to have noted that the prevailing winds were actually from the northeast, contrary to what he had expected. In correspondence with his brother, Franklin learned that the same storm had not reached Boston until after the eclipse, despite the fact that Boston is to the northeast of Philadelphia. He deduced that storms do not always travel in the direction of the prevailing wind, a concept that greatly influenced meteorology.
After the Icelandic volcanic eruption of Laki in 1783, and the subsequent harsh European winter of 1784, Franklin made observations connecting the causal nature of these two separate events. He wrote about them in a lecture series.
Traction kiting
Though Benjamin Franklin has been most noted kite-wise with his lightning experiments, he has also been noted by many for his using kites to pull humans and ships across waterways. The George Pocock in the book A TREATISE on The Aeropleustic Art, or Navigation in the Air, by means of Kites, or Buoyant Sails noted being inspired by Benjamin Franklin's traction of his body by kite power across a waterway. In his later years he suggested using the technique for pulling ships.
Concept of cooling
Franklin noted a principle of refrigeration by observing that on a very hot day, he stayed cooler in a wet shirt in a breeze than he did in a dry one. To understand this phenomenon more clearly Franklin conducted experiments. In 1758 on a warm day in Cambridge, England, Franklin and fellow scientist John Hadley experimented by continually wetting the ball of a mercury thermometer with ether and using bellows to evaporate the ether. With each subsequent evaporation, the thermometer read a lower temperature, eventually reaching 7 °F (−14 °C). Another thermometer showed that the room temperature was constant at 65 °F (18 °C). In his letter Cooling by Evaporation, Franklin noted that, "One may see the possibility of freezing a man to death on a warm summer’s day."
Temperature's effect on electrical conductivity
According to Michael Faraday, Franklin's experiments on the non-conduction of ice are worth mentioning although the law of the general effect of liquefaction on electrolytes is not attributed to Franklin. However, as reported in 1836 by Prof. A. D. Bache of the University of Pennsylvania, the law of the effect of heat on the conduction of bodies otherwise non-conductors, for example, glass, could be attributed to Franklin. Franklin writes, "...A certain quantity of heat will make some bodies good conductors, that will not otherwise conduct..." and again, "...And water, though naturally a good conductor, will not conduct well when frozen into ice."
Oceanography findings
An aging Franklin accumulated all his oceanographic findings in Maritime Observations, published by the Philosophical Society's transactions in 1786. It contained ideas for sea anchors, catamaran hulls, watertight compartments, shipboard lightning rods and a soup bowl designed to stay stable in stormy weather.