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Ben Franklin

Benjamin Franklin's Inventions, Discoveries, and Improvements


bifocalsA modern replica pair of the type of split bifocal spectacles known to have been worn by Benjamin Franklin in the mid 1780s

Bifocals are eyeglasses with an upper and lower half, the upper for distance, and the lower for reading. Bifocals are commonly prescribed to people with presbyopia, a condition that Franklin suffered. Franklin wrote, in August 1784 to his friend George Whatley, that he was "happy in the invention of double spectacles, which serving for distant objects as well as near ones, make my eyes as useful to me as ever they were."


Franklin did not, of course, invent electricity, but he discovered many things about it, previously not understood.

kiteFranklin's Kite Experiment

Before Franklin started his scientific experimentation, it was thought that electricity consisted of two opposing forces. Franklin showed that electricity consisted of a "common element" which he named "electric fire." Further, electricity was "fluid" like a liquid. It passed from one body to another — however it was never destroyed. In a letter to Peter Collinson, Franklin wrote that the "fire only circulates. Hence have arisen some new items among us. We say B (and other Bodies alike circumstanced) are electricised positively; A negatively; Or rather B is electricised plus and A minus ... These terms we may use till philosophers give us better."

Franklin's work became the basis for the single fluid theory. When something is being charged, such as a car battery, electricity flows from a positive body, that with an excess charge, to a negative body, that with negative charge. Indeed, a car battery has plus and minus signs on its terminals.

Franklin wrote Collinson in another letter that: "I feel a Want of Terms here and doubt much whether I shall be able to make this intelligible." Not only did Franklin have to posit theories, he also had to create a new language to fit them. Some of the electrical terms which Franklin coined during his experiments include:

  • battery
  • charge
  • condensor
  • conductor
  • plus
  • minus
  • positively
  • negatively
  • armature

They are still the terms we use today.

Lightning Rod

Franklin Institute
Rod believed to be an original of Franklin's

Once Franklin had an understanding of the behavior of electricity, he set about to protect houses from the destructive forces of lightning. A lightning rod, simply, is a rod attached to the top of a building, connected to the ground through a wire. The electric charge from lightning strikes the rod and the charge is conducted harmlessly into the ground. This protects houses from burning down and people from electrocution.

Franklin wrote, in 1753

It has pleased God in his goodness to mankind, at length to discover to them the means of securing their habitations and other buildings from mischief by thunder and lightning. The method is this: Provide a small iron rod (it may be made of the rod-iron used by the nailers) but of such a length, that one end being three or four feet in the moist ground, the other may be six or eight feet above the highest part of the building. To the upper end of the rod fasten about a foot of brass wire, the size of a common knitting-needle, sharpened to a fine point; the rod may be secured to the house by a few small staples. If the house or barn be long, there may be a rod and point at each end, and a middling wire along the ridge from one to the other. A house thus furnished will not be damaged by lightning, it being attracted by the points, and passing thro the metal into the ground without hurting any thing. Vessels also, having a sharp point rod fix'd on the top of their masts, with a wire from the foot of the rod reaching down, round one of the shrouds, to the water, will not be hurt by lightning.

Franklin Stove

Franklin's original design for the Franklin stove.

In colonial America, homes were warmed by a fireplace. The Franklin stove, invented in 1742, is a metal-lined fireplace that stands in the middle of a room. It has rear baffles for improved airflow. It provides more heat and less smoke than an open fireplace and uses less wood. This cast-iron furnace would radiate heat from the middle of the room in all directions, and the iron walls even absorbed heat, providing warmth to the room long after the fire went out.

Source: Franklin's Autobiography

In Order of Time I should have mentioned before, that having in 1742 invented an open Stove, for the better warming of Rooms and at the same time saving Fuel, as the fresh Air admitted was warmed in Entring, I made a Present of the Model to Mr. Robert Grace, one of my early Friends, who having an Iron Furnace, found the Casting of the Plates for these Stoves a profitable Thing, as they were growing in Demand. To promote that Demand I wrote and published a Pamphlet Intitled, An Account of the New-Invented pennsylvania fire places: Wherein their Construction and manner of Operation is particularly explained; their Advantages above every other Method of warming Rooms demonstrated; and all Objections that have been raised against the Use of them answered and obviated. &c. This Pamphlet had a good Effect, Govr. Thomas was so pleas’d with the Construction of this Stove, as describ’d in it that he offer’d to give me a Patent for the sole Vending of them for a Term of Years; but I declin’d it from a Principle which has ever weigh’d with me on such Occasions, viz. That as we enjoy great Advantages from the Inventions of others, we should be glad of an Opportunity to serve others by any Invention of ours, and this we should do freely and generously. An Ironmonger in London, however, after assuming a good deal of my Pamphlet, and working it up into his own, and making some small Changes in the Machine, which rather hurt its Operation, got a Patent for it there, and made as I was told a little Fortune by it. And this is not the only Instance of Patents taken out for my Inventions by others, tho’ not always with the same Success: which I never contested, as having no Desire of profiting by Patents my self, and hating Disputes. The Use of these Fireplaces in very many Houses both of this and the neighbouring Colonies, has been and is a great Saving of Wood to the Inhabitants.

Mapping the Gulf Stream

Franklin made eight voyages across the Atlantic Ocean (or, as it was known then, the Western Ocean) between the Colonies and Europe. He wondered why journeys eastward were faster than return trips. His curiosity led him to be the first to map the Gulf Stream. The Gulf Stream, along with the North Atlantic Drift, is the ocean current that originates in the Gulf of Mexico, exits through the Strait of Florida, and follows the eastern coastlines of the United States and Newfoundland before crossing the Atlantic Ocean.

Here is Franklin's original map of the Gulf Stream.


Swim Fins

Benjamin Franklin was an avid swimmer from a very young age. Throughout his life he consistently promoted its healthful benefits. At the ripe old age of 11 he invented a pair of swim fins. However, unlike today's foot flippers, these were attached to one's hands. His advocacy for swimming was recognized by his induction into the International Swimming Hall of Fame in 1968.

Franklin wrote, in March 1773

When a youth, I made two oval pallets, each about ten inches long, and six broad, with a hole for the thumb, in order to retain it fast in the palm of my hand. They much resembled a painter's pallets. In swimming I pushed the edges of these forward, and I struck the water with their flat surfaces as I drew them back. I remember I swam faster by means of these pallets, but they fatigued my wrists. I also fitted to the soles of my feet a kind of sandals, but I was not satisfied with them, because I observed that the stroke is partly given by the inside of the feet and the ankles, and not entirely with the soles of the feet.

Swim fins by Frenchman Louis de Corlieu, in 1933, similar in concept to Franklin's invention.

Glass Armonica

A popular entertainment in England in the early 18th century was playing music on upright wine goblets, with tones made by rubbing one's fingers around the lip of glasses filled with different quantities of fluid. In 1761, Franklin created a mechanized version, and called it the Armonica (after the Italian word for harmony.) Franklin worked with London glassblower Charles James to build his Armonica, and it had its world premiere in early 1762, played by Marianne Davies.


Franklin's foot-treadle-operated instrument held 37 glass bowls. The musician touched the rims of the bowls with fingered moistened from the water trough. The bowl-rims were color-coded, according to the note. For example, C's are red, D's orange, E's yellow, etc.

From "The Life of Benjamin Franklin" by Jared Sparks

After many trials he succeeded in constructing an instrument of a different form, more commodious, and more extended in the compass of its notes. His glasses were made in the shape of a hemisphere, with an open neck or socket in the middle, for the purpose of being fixed on an iron spindle. They were then arranged one after another, on this spindle, the largest at one end and gradually diminishing in size to the smallest at the other end. The tones depended on the size of the glasses. The spindle, with its series of glasses, was fixed horizontally in a case, and turned by a wheel attached to its larger end, upon the principle of a common spinning-wheel.

The performer sat in front of the instrument, and the tones were brought out by applying a wet finger to the exterior surface of the glasses as they turned round. He called it the Armonica, in honor of the musical language of the Italians, as he says in a letter to Beccaria, in which it is minutely described. For some time the Armonica was in much use. A Miss Davies acquired great skill in playing upon it. She performed in public, and, accompanied by her sister, who was a singer, she exhibited her skill in the principal cities of Europe, where she attracted large audiences, and the notice of distinguished individuals. The instruments were manufactured in London, and sold at the price of forty guineas each.

Flexible Urinary Catheter

In Franklin's day, catheters (tubes inserted through the urethra into the bladder to drain urine from the body) were rigid and quite painful. Franklin devised a catheter with a flexible tube. John, Ben's older brother, suffered from kidney stones, and so Ben found a way to ease some of the disconfort for his brother.


Franklin was curious as to how far he was traveling by carriage, in his role as postmaster, for his travels between Philadelphia and Boston.

While the concept of the odometer dates back to ancient times, Franklin did create his own version. The concept was to attach the device near the wheels of a carriage, determine the circumferance of the wheel and the number of revolutions required to travel a mile, and have the device register the distance traveled.


The Institute News (June-July 1949) describing the action of an odometer

When actuated from a carriage wheel having a circumference of thirteen and one-fifth feet, a mile was registered in each four hundred revolutions. If wired to the top of the front axle at the right hand side it was easily set in operation by a nub-type projection on a hub or spoke and the dials were readily visible to both driver and rider." This odometer consists of a series of cogs and wheels that measure distance as noted above. On top of the works is a flat metal plate that has a series of three circles. The left circle has a T above it and has numbers from 10 to 1 running counterclockwise around the circle (10 is in the noon position). The circle is white with black Arabic numerals. The center circle is slightly larger than the side circles and it has the numbers 100 to 10, in increments of 10, running counterclockwise around the circle (100 is in the noon position). The circle is white with red Arabic numerals. The right circle has an H above it and has numbers from 10 to 1 running clockwise around the circle (10 is at the noon position). The circle is white with black Arabic numerals. At the center of the central circle is a brass arrow; the one on the left is completely missing and the one on the right is only a flat disk.

Source: Benjamin Franklin Tercentenary

"Long Arm"


Franklin was a great lover of books. However, reaching books on high shelves was a challenge. So, in 1786, the ever resourceful Franklin solved the problem by inventing the "long arm," which is simply a wooden pole with a grasping claw at the end. Simple, clever, effective.

Philad. Feb. 12. 1786

Dear Jonathan,

I wrote to you a few Days since, and sent you 4 philosophical Papers, which I permitted your communicating to Mr. Bowdoin. As they are chiefly speculative and hypothetical, and, (except the Description of the long Arm, a new Instrument for taking down Books from high Shelves) contain little of practical Utility.

Air Bath, forerunner of air conditioning (False)

Benjamin Franklin loved to take "air baths," in the buff, opening the windows to let in the fresh air. Even to open the window to let in fresh air was worrisome to many, for fear of drafts. At the time, there was little awareness of the dangers of stale air and the value of fresh air inside. However, to assert that this practice presaged the invention of Air Conditioning is giving the very worthy Dr. Franklin too much credit.

Bulkhead (False)

Some credit Franklin with inventing the first bulkhead. What is true is that as early as 1784, he did recommend using the Chinese method, which had existed for centuries ("Garden of Strange Things," written in the 5th century, by Liu Jingshu, makes a reference to it). A bulkhead is an upright wall within the hull (body or frame) of a ship to increase the structural rigidity of the vessel and to create watertight compartments, in the case of an accident. The term "bulkhead" was later applied to aircraft, spacecraft, as well as to fuel tanks.

Daylight Saving Time (False)


Franklin is often given credit for inventing Daylight Saving Time. He did write a satiric (never published) piece by that title, reproduced below. In this very funny piece, he claims credit for discovering the fact that the sun begins shining from the moment it rises, something that the locals, who sleep till noon, would never have means of knowing. To save on wasteful candles, Franklin recommends taxing people who use shutters, and of ringing bells every morning at sunup to force people to adjust their days according to the availability of sunlight.

Modern Daylight Saving Time dates to the late 19th century.

Proposal re Daylight Saving

[April 26, 1784]


As I perceive that your plan admits of communications from strangers, I beg leave to present you with an oeconomical project, attributed to a personage much celebrated for his superior talents in politics and philosophy. A translation of it appeared in one of the daily papers of Paris about the year 1784. What I now send you, is the original piece, with some additions and corrections made in it by the author.

As we are frequently disposed in this nation to engage in wars, and are sometimes embarrassed in what manner to raise money by taxes, I flatter myself that some ingenious statesman will improve upon the plan suggested in the following paper, and after altering it to the meridian of our island, bring it forwards as a scheme of finance. William the conqueror is said to have given considerable offence to our ancestors by a law for extinquishing lights and fires after a certain hour in the evening; but as the curfew was established by a foreign prince to enable him to abtain a more complete dominion over this country, and not by our native rulers for the purpose of enabling us to obtain dominion over other countries; a difference in circumstances that is so essential, cannot escape a discerning public. By the help of the savings that must occur from adopting the project in question in its full extent, it is hoped that we shall easily become the terror of nations. In any event, it may allow us to abolish various taxes that are a burthen upon the public, and above all upon the poor, and especially that singular tax imposed in this country upon our use of the light of the sun, so opposite to the project here proposed. The payment of our national debt is another object that may readily be accomplished by it. And the scheme has this farther recommendation attending it, that notwithstanding the distress of France in matters of revenue, and notwithstanding the late rapid changes of its administrations, no minister in that country, where the hint was originally made public, has appeared willing to adopt it; which promises us exclusive advantages from it in this country, should we prudently adopt it here. I am, Sir, your’s, &c.


To the Authors of the Journal


You often entertain us with accounts of new discoveries. Permit me to communicate to the public through your paper, one that has been late made by myself, and which I conceive may be of great utility.

I was the other evening in a grand company, where the new lamp of Messrs. Quinquet and Lange was introduced, and much admired for its splendor; but a general enquiry was made, whether the oil it consumed was not in proportion to the light it afforded, in which case there would be no saving in the use of it. No one present could satisfy us in this point, which all agreed ought to be known, it being a very desireable thing to lessen, if possible, the expence of lighting our apartments, when every other article of family expence was so much augmented.

I was much pleased to see this general concern for oeconomy; for I love oeconomy exceedingly.

I went home, and to bed, three or four hours after midnight, with my head full of the subject. An accidental sudden noise waked me about six in the morning, when I was surprized to find my room filled with light; and I imagined at first that a number of those lamps had been brought into it; but rubbing my eyes I perceived the light came in at the windows. I got up and looked out to see what might be the occasion of it, when I saw the sun just rising above the horizon, from whence he poured his rays plentifully into my chamber, my domestic having negligently omitted the preceding night to close the shutters.

I looked at my watch, which goes very well, and found that it was but six o’clock; and still thinking it something extraordinary that the sun should rise so early, I looked into the almanack, where I found it to be the hour given for his rising on that day. I looked forward too, and found he was to rise still earlier every day till towards the end of June, and that at no time in the year he retarded his rising so long as till eight o’clock. Your readers, who with me have never seen any signs of sun-shine before noon, and seldom regard the astronomical part of the almanack, will be as much astonished as I was, when they hear of his rising so early; and especially when I assure them that he gives light as soon as he rises; I am convinced of this. I am certain of my fact. One cannot be more certain of any fact. I saw it with my own eyes. And having repeated this observation the three following mornings, I found always precisely the same result.

Yet so it happens, that when I speak of this discovery to others, I can easily perceive by their countenances, though they forbear expressing it in words, that they do not quite believe me. One indeed, who is a learned natural philosopher, has assured me that I must certainly be mistaken as to the circumstance of the light coming into my room; for it being well known, as he says, that there could be no light abroad at that hour, it follows that none could enter from without; and that of consequence my windows being accidentally left open, instead of letting in the light, had only served to let out the darkness; and he used many ingenious arguments to shew me how I might by that means have been deceived. I own that he puzzled me a little, but he did not satisfy me; and the subsequent observations I made, as above-mentioned, confirmed me in my first opinion.

This event has given rise in my mind to several serious and important reflections. I considered that if I had not been awakened so early that morning, I should have slept six hours longer by the light of the sun, and in exchange have lived six hours the following night by candle light; and the latter being a much more expensive light than the former, my love of oeconomy induced me to muster up what little arithmetic I was master of, and to make some calculations, which I shall give you, after observing that utility is, in my opinion, the test of value in matters of invention, and that a discovery which can be applied to no use, or is not good for something, is good for nothing.

I took for the basis of my calculation the supposition that there are 100,000 families in Paris, and that these families consume in the night half a pound of bougies, or candles, per hour. I think this a moderate allowance, taking one family with another; for though I believe some consume less, I know that many consume a great deal more. Then estimating seven hours per day, as the medium quantity between the time of the sun’s rising and ours, he rising during the six following months from six to eight hours before noon; and there being seven hours of course per night in which we burn candles, the account will stand thus:

In the six months between the 20th of March and the 20th of September, there are Nights,183
Hours of each night in which we burn candles,7
Multiplication gives us for the total number of hours,1,281
These 1281 hours, multiplied by 1000,000, the number of families, give128,1000,000
One hundred twenty-eight millions and one hundred thousand hours, spent at Paris by candle-light, which at half a pound of wax and tallow per hour, gives the weight of64,050,000
Sixty-four millions and fifty thousand of pounds, which, estimating the whole at the medium price of thirty sols the pound, makes the sum of ninety-six millions and seventy-five thousand livres tournois,96,075,000

An immense sum! that the city of Paris might save every year, only by the oeconomy of using sun-shine instead of candles.

If it should be said that people are apt to be obstinately attached to old customs, and that it will be difficult to induce them to rise before noon, consequently my discovery can be of but little use; I answer, nil desperandum, I believe all who have common sense, as soon as they have have learnt from this paper that it is day-light when the sun rises, will contrive to rise with him; and to compel the rest, I would propose the following regulations:

First. Let a tax be laid of a louis per window, on every window that is provided with shutters to keep out the light of the sun.

Second. Let the same salutary operation of police be made use of to prevent our burning candles that inclined us last winter to be more oeconomical in burning wood; that is, let guards be placed in the shops of all the wax and tallow chandlers, and no family permitted to be supplied with more than one pound of candles per week.

Third. Let guards also be posted to stop all the coaches, &c. that would pass the streets after sun-set, except those of physicians, surgeons, and midwives.

Fourth. Every morning, as soon as the sun rises, let all the bells in every church be set ringing; and if that is not sufficient, let cannon be fired in every street, to wake the sluggards effectually, and make them open their eyes to see their true interest.

All the difficulty will be in the first two or three days; after which the reformation will be as natural and easy, as the present irregularity: for ce n’est que le premier pas qui coute. Oblige a man to rise at four in the morning, and it is more than probably he shall go willingly to bed at eight in the evening; and having had eight hours sleep, he will rise more willingly at four the morning following.

But this sum of ninety-six millions and seventy-five thousand livres, is not the whole of what may be saved by my oeconomical project. You may observe, that I have calculated upon only one-half of the year, and much may be saved in the other, though the days are shorter. Besides the immense flock of wax and tallow left unconsumed during the summer, will probably make candles much cheaper for the ensuing winter, and continue cheaper as long as the proposed reformation shall be supported.

For the great benefit of this dixcovery, thus freely communicated and bestowed by me on the public, I demand neither place, pension, exclusive privilege, or any other reward whatever. I expect only to have the honour of it. And yet I know there are little envious minds who will, as usual, deny me this, and say that my invention was known to the antients, and perhaps they may bring passages out of old books in proof if it. I will not dispute with these people that the antients might know the sun would rise at certain hours; they possibly had, as we have, almanacks that predicted it; but it does not follow from thence that they knew he gave light as soon as he rose. This is what I claim as my discovery. If the antients knew it, it must have been long since forgotten, for it certainly was unknown to the moderns, at least to the Parisians, which to prove, I need use but one plain simple argument. They are as well-instructed, judicious, and prudent a people as exist any where in the world, all professing like myself to be lovers of oeconomy; and from the many heavy taxes required from them by the necessities of the state, have surely an abundant reason to be oeconomical. I say it is impossible that so sensible a people, under such circumatances, should have lived so long by the smoaky unwholesome and enormously-expensive light of candles, if they had really known that they might have had as much pure light of the sun for nothing. I am, &c.

An Abonne.

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