Let's do a historical #OpticsLessonOfTheDay on the birthday of my favorite scientist ever, Michael Faraday (1791-1867)! Though he is relatively unknown to the public, he is inarguably one of the greatest scientists who ever lived... and an amazing person, as well. 
By societal standards of the time, Faraday should have lived a mundane, uneventful life. He was born the son of a blacksmith in Surrey in the UK. He was raised with little formal education, and was apprenticed to a bookbinder at age 14.
But working at a bookshop gave Faraday access to lots of books, including science books, and his master George Ribeau was a decent fellow who gave Faraday leisure time to indulge his curiosity.
Faraday's first significant science book was a 1797 encyclopedia volume with an article on electricity. Faraday was intrigued, and spent some of his meager savings on equipment to test experiments he had read about.
The most important book in Faraday's life arrived at the bookshop in 1810: Conversations on Chemistry, written by Jane Marcet. Marcet learned some chemistry at home with her physician husband, and attended chemistry lectures at the Royal Institution by the famed Humphry Davy...
Marcet decided she wanted to write a book on chemistry that would be accessible to women like her who possessed no formal science education. The book came out in 1805, and was a huge success: it went through 16 editions.
Incidentally, you can still buy reprints of Marcet's book. I recommend getting a copy of this heavy book and carrying it with you. That way, if you ever encounter someone who says "women don't contribute to science," you can beat them with it. (More on Marcet in a bit.)
Okay, lunch in a minute, so I'll continue this afterwards.
Update: I will finish this thread, but got distracted by work. More later.
Where was I? Oh, yes; Faraday and Jane Marcet's book. Faraday devoured its contents and verified every experiment he could. He so impressed patrons of the bookshop that one got him tickets to see Humphry Davy's lectures.
Faraday took detailed notes at Davy's lectures, and was encouraged to ask Davy about job prospects at the Royal Institution where Davy worked; he sent along his notes with his inquiry. Davy responded positively, and offered Faraday a job as Chemical Assistant. (pic of Davy)
Faraday had hardly started when he got an even greater opportunity: Davy was planning a European tour, but was short a valet, and asked Faraday if he would come along in the dual role of valet and chemical assistant. Faraday jumped at the chance.
The trip was a success for Faraday -- he got to meet the greatest scientists in Europe, and impressed them with his talent and thoughtfulness. His one struggle was with Mrs. Davy, who considered him more a servant and treated him as such...
When Davy and Faraday got to have dinner with the Marcets, Faraday was mortified when he was told by Mrs. Davy to eat in the kitchen with the servants. After the meal, when the ladies had left, Marcet's husband said "let us go and join Mr. Faraday in the kitchen."
Faraday's trip lasted several years, beginning in 1813. When he returned to England, he dove into his job at the Royal Institution with vigor. In 1825, he was made Director of the Laboratory, and in 1833 he was made the Fullerian Professor of Chemistry at the RI.
Starting in 1820, Faraday devoted himself to electrical experiments. In 1820, Hans Christian Oersted had shown that an electric current can deflect a compass needle, showing that electricity and magnetism are related. This discovery was an international sensation.
Studying this effect, in 1821 Faraday invented the first electric motor, called the homopolar motor, in which the wire (on the right) circulates around the central magnet while powered by a chemical battery.
In 1831, Faraday began a long-running series of publications on his experimental results, called "Experimental Researches in Electricity." In his very first paper, he announced his most famous result: the discovery of electromagnetic induction.
Oersted had shown that an electrical current could influence a magnet; Faraday, like many others, wondered if in reverse a magnet could "induce" a current to flow. At first it seemed the answer was "no": a steady magnet didn't seem to cause a current.
But let's look at Faraday's crucial experiment. He wrapped two separate coils of wire around a cylinder of wood. One coil went to a battery, and the other went to a current meter (galvanometer)...
Turning the current on would cause a powerful magnetic field to flow through the black coil; Faraday wanted to see if this magnetic field caused a current to flow through the red coil. The answer was no, EXCEPT...
Faraday found that the gavanometer showed a slight reading was produced whenever the battery current was turned on or off. Just a little twitch of the needle while the current started or stopped.
Faraday had discovered that a *changing* magnetic field will create a circulating electric field, one that can drive a current in a wire. This effect is often called Faraday induction. Faraday had shown that electricity and magnetism were related in more than one way!
Faraday would do much more in the course of his electrical researches. He worked hard to show that all types of electricity -- whether produced from static electricity, chemicals, or from animals, were the same. Basically he showed that all sources can do the same things.
To test animal electricity, he and his assistants would literally place their hands on electric eels and try to quantify how much they were shocked! They eventually came up with a set of paddles to make things easier.
Faraday's other famous achievement is what is now known as Faraday rotation. Having shown that electricity and magnetism are related, he wanted to show that light and magnetism are somehow related...
The experiment that finally worked involved sending polarized light through a sample liquid which also had a magnetic field applied. Faraday found that, under the influence of the magnet, the light polarization direction rotates.
Note: Faraday made this discovery in 1845, when he was 54 years old! Don't let anyone tell you science is only for the young.
Faraday was a thorough experimenter. After he found rotation with one sample, he wanted to confirm that it was a universal effect, and not an artifact somehow of his sample. He tested and confirmed rotation in 150 fluids he had in his lab!
Faraday was a brilliant experimentalist, but had little mathematical training and was not a strong theorist. Nevertheless, he made one huge contribution to theory in 1852 -- AT AGE 61!
Remember that picture showing Faraday induction using arrows to represent what we now call electric and magnetic "fields"? Faraday introduced this idea that charges and magnets produce fields that then interact with other charges and magnets.
This was a big departure from the mathematical approach, which largely consisted of "action at a distance": imagining two charges or magnets interact directly at a distance. Faraday instead imagined them interacting through fields.
He was inspired by the traditional demonstration of iron filings around a bar magnet. Faraday saw "fields" as a better way to understand electromagnetic interactions.
Faraday's fields gathered little attention at first. But a Scottish physicist named James Clerk Maxwell saw in them a way to mathematical describe electricity and magnetism in an effective way.
In 1861, Maxwell realized that the existing equations of electromagnetism were missing a piece, and inherently inconsistent...
The missing piece? Maxwell found that just as a time-varying magnetic field should induce a circulating electric field, a time-varying electric field should induce a circulating magnetic field!
Even more important: when this missing piece is added to the electromagnetic equations, those equations predict that electromagnetic waves must exist that travel at the speed of light. Maxwell argued, correctly, that light must be an electromagnetic wave!
Maxwell's great discovery can be traced back to Faraday's demonstration of the link between light, electricity, and magnetism, and his introduction of fields. In his 1873 book, Maxwell wrote fondly of Faraday's contributions:
Faraday had amazing intuition. In 1851, he wondered if gravity might be able to induce an electric current just as magnetism did? His experiments failed, but represented an amazing faith in the interconnectedness of physical phenomena.
Of his gravity experiments, he wrote: "ALL THIS IS A DREAM. Still examine it by a few experiments. Nothing is too wonderful to be true, if it be consistent with the laws of nature; and in such things as these, experiment is the best test of such consistency."
Faraday also cared about the environment. In 1855, he wrote a letter to The Times expressing concern at the polluted state of the Thames, which led to this famous Punch cartoon.
As a Professor at the Royal Institution, Faraday gave many popular science lectures at Christmastime; the Christmas Lectures continue to this day. Two of Faraday's were published, and are still incredibly enjoyable to read today.
Whew! Let me wind down by noting that Faraday stayed lifelong friends with Jane Marcet, corresponding with her about any new discoveries he made. He gave her full credit for her role in his success and his career:
So much more I could say, but let me stop here, as it is getting late and I am tired. Happy birthday and rest in peace, Michael Faraday, you amazing scientist and human! /END
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