Lived 1706 – 1790.
Benjamin Franklin lived his life in the spirit of a renaissance man: he was deeply interested in the world around him, and he excelled in several widely differing fields of human endeavor.
He had a profound effect on our understanding of electricity and shaped the language we use when we talk about it, even today.
Here we shall concentrate on his life as a scientist and an inventor, only briefly touching on his other achievements.
Benjamin Franklin’s Early Life and EducationBenjamin Franklin was born on January 17, 1706, in Boston, Massachusetts. His father, Josiah, was a tallow chandler, candle maker, and soap boiler who had moved to the American Colonies from England. His mother, Abiah Folger looked after the home and was the mother of ten children, including Benjamin, who was the eighth child in the family. She was born in Nantucket, Massachusetts.
Benjamin only had two years of formal education, which finished when he was ten years old, because his family could not afford the fees. His informal education then accelerated, because his mind was too restless to stop learning.
He had to work in his father’s business, but in his spare time he read everything he could, about every subject under the sun.
When he was twelve, Benjamin began working as an apprentice in a printing shop owned by one of his elder brothers, James. When his brother started printing a newspaper, Benjamin wrote to it in the name of “Mrs. Dogood” in defense of freedom of speech.
Aged 17, Benjamin Franklin left for Philadelphia, escaping from his apprenticeship, which was against the law. He was, however, free. After a few months in Philadelphia he left for London, England, where he learned more about printing, before returning to Philadelphia at the age of 20 to continue his career in printing.
Benjamin Franklin – PublisherBy the age of just 23, Franklin had become the publisher of the Philadelphia Gazette.
Aged 27, in December 1732, the first editions of the publication that would make him a wealthy man rolled off his printing press: Poor Richard’s Almanac, which Franklin would publish annually for the next 25 years. It was a general interest pamphlet offering interest and amusement for its readers, including: ‘how to’ guides, practical tips, stories, astrological forecasts, and brain teasers.
With each year he published the Almanac, his financial position grew more secure, and Franklin’s fertile mind began looking for new outlets.
He continued reading as much as he could, increasing his knowledge of science and technology until he was in a position to begin innovating himself.
Benjamin Franklin’s Science, Innovation, and InventionsFranklin was an original thinker, scientist and inventor. Dating his inventions is not always easy, because Franklin did not patent what he invented. He said that anyone who wanted to make money from his ideas was free to do so. This means the dates given to his inventions are approximate.
Bifocal SpectaclesFranklin wore spectacles for most of his life.
He felt limited by the spectacles of his day, because a lens that was good for reading blurred his vision when he looked up. Working as a printer, this could be infuriating.
He defeated this problem in about 1739, aged 33, with his invention of split-lens bifocal spectacles. Each lens now had two focusing distances. Looking through the bottom part of the lens was good for reading, while looking through the upper part offered good vision at a greater distance.
The Franklin StoveAs Franklin read more about science, he learned more about heat transfer. He looked at the design of a typical stove and concluded that it was inefficient. Much more heat was lost up the flue than necessary.
He decided to redesign the stove using the concept of heat-exchange/heat recovery.
The idea was that hot gases which would normally simply go up the flue would exchange their heat with cold air from the room, heating it up, and so heating the room up.
In 1741, the Franklin Stove came on to the market, allowing homeowners to get more heat into their homes for each unit of fuel they burned.
Cold air (blue) gains heat from contact with the hot stove. As this warming air continues on its path, it gains more heat through contact with metal, the other side of which is in contact with the hot smoke (red) going to the flue.
The use of these fireplaces in very many houses, both of this and the neighboring colonies, has been, and is, a great saving of wood to the inhabitants.
American Philosophical SocietyIn 1743, Franklin founded the American Philosophical Society. (In those days, scientists were called philosophers.) The Society offered a scientific forum for new ideas, including Franklin’s electrical theories.
The Size of the Units of MatterBenjamin Franklin performed a beautiful experiment using surfactants; on a pond at Clapham Common, he poured a small amount of oleic acid, a natural surfactant which tends to form a dense film at the water-air interface. He measured the volume required to cover all the pond. Knowing the area, he then knew the height of the film, something like three nanometers in our current units.
Pierre-Gilles de Gennes, 1932 to 2007
ElectricityIn summer 1743, Franklin visited his hometown of Boston. Always seeking new knowledge, he visited a science show. There he saw Dr. Archibald Spencer, who had arrived from Scotland, demonstrating a variety of scientific phenomena. The electrical part of the show intrigued Franklin most: it featured the effects of static electricity.
Franklin left the show determined to learn more about electricity. It seemed to him that Dr. Spencer didn’t really understand it. This, of course, was true: nobody understood it! It was more a source of entertainment than a science.
In 1747, Franklin got hold of a long glass tube for the efficient generation of static electricity from Peter Collinsion in London.
Soon, Franklin was spending much of his time studying electricity. He wrote:
“For my own part, I never was before engaged in any study that so totally engrossed my attention and my time as this has lately done.”
Shaping our understanding of electricityFranklin’s observations soon began to shape the world’s understanding of electricity and shape the language we use even today when we talk about it.
He identified that there was an electrical fluid that could flow from A to B. To describe the process he coined the terms positive and negative to describe the difference between A and B after the electrical fluid had flowed. Of course, today we would call the electrical fluid electrons, but remember: this was 1747; J.J. Thomson’s discovery of the electron lay 150 years in the future!
Franklin found that an excess of fluid led to positive charge (okay, we’ll have to pretend that electrons are positively charged for this) and a deficit of fluid led to negative charge.
Franklin was the first to write that electric charge cannot be created; it can only be ‘collected.’ This is a fundamental law of physics – the Law of Conservation of Electric Charge. It means that you cannot create (or destroy) electric charge.
Franklin was also the first person to use the words electrical battery. His meaning was not the same as ours though. His battery was made of capacitors (known as Leyden jars) wired together in series to store more charge than one alone could. This enabled Franklin to produce a bigger discharge of static electricity in his experiments.
In 1751, Franklin published the fruits of his labors in a book called Experiments and Observations on Electricity, which was widely read in Britain and then Europe, shaping a new understanding of electricity.
In 1752 Franklin’s most famous scientific work was carried out – the proof that lightning is electricity.
Franklin had an idea for an experiment to prove that lightning is electricity, making use of another of his own discoveries in electricity: that static electricity discharges to a sharp, pointed object more readily than to a blunt object.
And now here are Benjamin Franklin’s own words on the subject:
From Benjamin Franklin’s Experiments and Observations on Electricity
“As electrified clouds pass over a country, high hills and high trees, lofty towers, spires, masts of ships, chimneys, etc, as so many prominences and points, draw the electrical fire, and the whole cloud discharges there…
“If these things are so, may not the power of points be of use to mankind, in preserving houses, churches,… from the stroke of lightning, by directing us to fix on the highest parts of those edifices, upright rods of iron made sharp as a needle… and from the foot of those rods a wire down the outside of the building into the ground…?
Benjamin Franklin’s Proposed Sentry Box“I would propose an experiment… On the top of some high tower or steeple, place a kind of sentry-box big enough to contain a man and an electrical stand. From the middle of the stand, let an iron rod rise and pass bending out of the door, and then upright 20 or 30 feet, pointed very sharp at the end. If the electrical stand be kept clean and dry, a man standing on it when such clouds are passing low might be electrified and afford sparks, the rod drawing fire to him from a cloud. If any danger to the man should be apprehended (although I think there would be none) let him stand on the floor of his box, and now and then bring near to the rod a loop of wire that has one end fastened to the leads he his holding by a wax handle; so the sparks, if the rod is electrified, will strike from the rod to the wire and not affect him.”
King Louis XV saw a translation of Experiments and Observations on Electricity, and he asked French scientists to test Franklin’s lightning rod concept.
Jean Francois Dalibard used Franklin’s idea to confirm by experiment that lightning was indeed electrical in Paris in May 1752. Franklin himself carried out similar work in 1752, using a kite with a metal key connected to a Leyden Jar to prove his own theory. He didn’t write about his own experiment, however, until 1772.
The significance of the experiment was that it established the study of electricity as a serious scientific discipline.
Franklin had shown how to prove that electrical phenomena were a fundamental force of nature. Electricity would never again be thought of as just an interesting plaything for scientists and showmen to conjure up using glass rods.
Very soon, in 1753, when he was aged 47, the transformation in science that Franklin had brought about was recognized. Britain’s Royal Society honored his electrical work with its highest award, the Copley Medal – the equivalent of a modern Nobel Prize.
The Lightning Rod
A building protected by a lightning rod. A cable carries electricity from lightning to ground.
Even today, we still use Benjamin Franklin’s lightning rod.
Like his other ideas, he did not patent it: he profited from the lightning rod intellectually, not financially.
Since the time he invented it, it has saved societies all over the world great amounts of time and money by protecting buildings from damage. It has also, of course, saved countless lives.
RefrigerationIn 1758, working with John Hadley in Cambridge, England, Franklin investigated the principle of refrigeration by evaporation.
In a room at 18 °C (65 °F) , the scientists repeatedly wetted a thermometer with ether, then used bellows to quickly evaporate the ether.
They were finally able to achieve a temperature reading on the thermometer of -14 °C (7 °F).
We now know the reason for the refrigeration effect. We have learned that molecules in a liquid have a range of energies. Some have high energy, and some have low energy. Molecules carrying the most energy escape from the liquid most easily – they evaporate. This leaves the lower energy, colder molecules in the liquid. The result is that the temperature of the liquid falls.
Of his discovery, Franklin said:
“One may see the possibility of freezing a man to death on a warm summer’s day.”
In fact, the principle of cooling by evaporation had been publicly demonstrated by William Cullen in Edinburgh, Scotland in 1756. Cullen had used a pump to lower the pressure above ether in a container.
The reduced pressure caused the ether to evaporate rapidly through boiling, absorbing heat from the air around it, and causing some ice to form on the container sides.
MeteorologyBy observation of storms and winds, Franklin discovered that storms do not always travel in the direction of the prevailing wind. This was an important discovery in the development of the scientific discipline of meteorology.
More than a Scientist and InventorFranklin lived in turbulent times, which culminated in the United States’ Declaration of Independence in 1776: Franklin was one of the five men who drafted it. He had previously acted as British postmaster for the colonies; he was the American Ambassador in France from 1776 – 1785; and the governor of Pennsylvania from 1785 – 1788.
The EndBenjamin Franklin died on April 17, 1790, at the age of 84. He was killed by pleurisy – a lung inflammation.
His wife, Deborah, had died sixteen years earlier. Franklin was survived by his daughter, Sarah, who looked after him in his later years and his son, William. William left America to live in Britain in 1782.
Today, the Benjamin Franklin Medal, named in Franklin’s honor, is one of the most prestigious awards in science. Its winners include Alexander Graham Bell, Marie and Pierre Curie, Albert Einstein and Stephen Hawking.