Initial Conditions Episode 9: The Unexpected Hero of Light

Find the corresponding podcast episode here: Initial Conditions - A Physics History Podcast

In 2014, the mantis shrimp was all the rage. Specifically, the fact that these crustaceans have twelve different types of photoreceptors in their eyes compared to humans’ meager three. “If we can see the rainbow with our humble eyes, what can these shrimp see?,” asked academic researchers, college admissions essays, and Tumblr teens alike. What could we learn if we could see light in a different way? Well unfortunately, it turns out mantis shrimp actually see fewer colors than humans. Still, humans have had a mantis shrimp mythology moment. 

Until the late 19th century, human understanding of light was limited. Slowly, throughout the century, new wavelengths of light were discovered, more high precision measurements of the speed of light were possible, and a new field of physics dedicated to separating light into its different components emerged. Spectroscopy, as this field is called, enables us to decode all the information light carries by splitting light into different spectral components. Instead of merely cataloging the brightness of stars in the sky, astronomers could use the light that reaches their telescopes to learn incredible things: like what elements the star is made of, how quickly it is moving, the direction of its motion, and even whether or not a planet is orbiting it. “Yesterday, my life was duller // now everything’s technicolor,” Lizzie McGuire once wrote about the discovery of the electromagnetic spectrum and its implications for astronomy. The combination of astronomy and spectroscopy created the field of astrophysics and is the basis for almost everything we know about the universe. In many ways, through spectroscopy, we have the mantis shrimp vision we so desperately craved a decade ago.

But there is an elephant (did you know elephants are colorblind?) in the room when it comes to the discussion of the history of light: how does it travel? Debates surrounding whether light is a particle or a wave (or both) implied, for nineteenth century physicists, that light traveled through a medium called the luminiferous aether. However, the parameters for this aether were inconsistent and never observed directly. One experiment is generally credited for ruling out the aether. The 1887 Michelson-Morley Experiment demonstrated that regardless of the direction light traveled, its velocity was unaffected. If this sounds to you like “the speed of light is constant,” special relativity jargon, then you are on the right track. Many believe that this experiment and the resulting abandonment of the luminiferous aether is the foundation of modern physics.

Albert Michelson (1852-1931) was a physicist best known for his work studying the properties of light.

Credit: Photograph by Florence M. Hendershot, Michelson Collection, Nimitz Library, U. S. Naval Academy, courtesy of AIP Emilio Segrè Visual Archives. Catalog ID: Michelson Albert A8

Some physicists held on tight to the aether, like a physics security blanket. Incidentally, Albert Michelson, the light-measuring protégé behind the experiment that killed the aether, never fully abandoned the aether. His feelings are understandable: his career was built on his unique connection with light and his unparalleled ability to measure it. 

Born to Jewish parents in 1852 in Strelno, Prussia, Albert’s family fled religious persecution and immigrated to the United States when he was only two, settling in a mining town 150 miles east of San Francisco. After graduating from the Naval Academy, Albert became a physics and chemistry teacher at the Academy. A textbook perfectionist, he was committed to measuring the speed of light with ever higher precision. Naturally, he was also interested in measuring the luminiferous aether, the medium in which his beloved light supposedly traversed. He specifically investigated the relative velocity of Earth through the aether, assuming the aether was a stationary fluid that the Earth speeds through, like a boat on a lake. He created an interferometer, a high precision device that splits a beam of light in two perpendicular directions, bounces the light off mirrors, and recombines it. If the waves of light were offset from traveling in different directions through the aether, the interferometer would show a distinctive interference pattern. However, Albert did not find the interference pattern he expected and concluded that his instrument was not precise enough to measure the subtle aether. 

Continuing his lifelong quest for precision, Albert, now at the Case School of Applied Science in Cleveland, Ohio, teamed up with Edward Morley, a chemist at the Western Reserve University. Together they worked to minimize all experimental uncertainties possible. They added mirrors to increase the distance light traveled, theoretically increasing the impact of the aether. They mounted the interferometer on a shallow pool of mercury and rotated it to measure the impact of the orientation of the device. They conducted measurements over the course of many months in case Earth’s orbital position mattered. They even conducted their experiments at night to limit the impact of foot traffic on the apparatus. Most significantly for the purpose of this episode, they recruited the promising lens-maker, John Brashear. Yet, Michelson and Morley returned one of the most important negative results in the history of physics: there was no detectable aether. They both continued measuring light and in 1907, Albert was awarded the Nobel Prize in physics "for his optical precision instruments and the spectroscopic and metrological investigations carried out with their aid."

Diagram of the Michelson Interferometer used in the Michelson Morley experiment of 1887 from their paper On the Relative Motion of the Earth and the Luminiferous Ether

This blog post is not to tell the story of Albert Michelson, but of the man whose lenses facilitated the success of Michelson’s apparatuses and were used in groundbreaking spectroscopic observations. That man is John Brashear. Uncle John, as he was known to many, was born November 24, 1840, in Brownsville, Pennsylvania, 35 miles down the Monongahela River from Pittsburgh. Under the mentorship of his grandfather, he fell in love with the night sky.

John Brashear (1840-1920) contributed to physics through his high precision lenses and mirrors.

Credit: AIP Emilio Segrè Visual Archives, Catalog ID: Brashear John A1

I have a confession to make here: I knew about Brashear because I attended the University of Pittsburgh and conducted undergraduate research out of the Allegheny Observatory. For both institutions, John Brashear is something of a legend. His legacy is immensely felt, especially at the observatory, so I feel very connected to his story. If you listen closely enough to the episode, you might hear when I start crying!

John was deeply religious and even briefly pursued a career as a minister, but ultimately moved to Pittsburgh to become a millwright in a steel mill. He was a talented machinist and quickly rose through the ranks despite his basic, elementary education. Meanwhile, he was falling madly in love with Phoebe Stewart, a Sunday school teacher. They secretly married in 1862 because her family disapproved, but were eventually discovered when her mother caught them kissing in the family kitchen. Scandalous! The happy couple moved into a modest house in Pittsburgh and started working on their shared passion project: building a telescope so they could stargaze. They assembled a makeshift workshop in their backyard and John started collecting books so he could learn everything about lens making. Every free minute (of which there were few, given steel workers often worked 12 hour days, seven days a week) was dedicated to lens-making.

For two years, John meticulously polished a five inch lens. When it was perfect, he held it to the light. And dropped it. He was devastated, but Phoebe encouraged him to try again. He regularly corresponded with the Director of the Allegheny Observatory, Samuel Pierpont Langley, who was later Secretary of the Smithsonian Institution and a well known astronomer. When the second lens was completed, John marched up the hill to the Allegheny Observatory with his lens wrapped in a bandana, and showed it to the Director. Langley was so impressed that he introduced John to the Observatory’s benefactor and railroad tycoon, William Thaw. Thaw sponsored John’s work while Langley, and the Allegheny Observatory, became a valued customer.

Samuel Pierpoint Langley, Director of the Allegheny Observatory, who first mapped in great detail and with high precision the infra-red radiations reaching the earth from the sun.

Credit: AIP Emilio Segrè Visual Archives Catalog ID: Langley Samuel A1

Quickly, John’s operation grew in Brashear Lens Co. and he employed his son-in-law, James McDowell and started collaborating with the Yale physicist, Charles Hastings and the Johns Hopkins physicist Henry Rowland. They made some of the largest telescope lenses on the market and the most precise diffraction gratings and custom optics. These lenses helped separate light from distant stars into spectral components and ushered in the age of astrophysics. It was no surprise then, that Albert Michelson recruited him to make the lenses for his interferometer to measure the luminiferous aether. The lens that John built for the Michelson interferometer was dubbed “the flattest surface on Earth.” Despite his humble beginnings, John Brashear became one the most sought after lensmakers in the world. 

John Brashear working on a 72 inch mirror for the Dominion Astrophysical Observatory, circa 1915.

Credit: University of Pittsburgh

Meanwhile, John worked to make astronomy more accessible to the general public. His first workshop and telescope were open to neighbors and children were constantly running about. He wrote an astronomy column in the local newspaper and gave free lectures. He also volunteered at a local prison, bringing his telescopes so the inmates would not forget the night sky. John served on the board of a school for blind children where he told the children stories about the stars so they too could share passion. He temporarily (and begrudgingly) served as director of the Allegheny Observatory where he helped raise the funds to relocate the observatory. After much pleading from the Western University of Pennsylvania (today the University of Pittsburgh) he also served as Chancellor of the University. It was an intimidating role–he never received higher education, but quickly everyone became family. Somehow, he also had free time to serve on the board of multiple charitable organizations. Still, John was never wealthy because he refused to charge for most of his services. Even when he was making lenses he rarely charged enough to cover the supplies, let alone labor. To him, the sky was for everyone and there should not be a barrier like money preventing people from experiencing it the way he did. 

John Brashear was much loved by those who knew him. For his 75th birthday celebration, the giant Soldiers and Sailors Memorial Hall was overwhelmed when 700 people showed up. When he passed away on April 8th, 1920, flags in Pittsburgh were lowered to half staff. His ashes were combined with Phoebe’s and placed in the crypt of the Allegheny Observatory he helped build. Their epitaph quotes the Sarah William poem, An Astronomer to His Pupil. It reads “we have loved the stars too fondly to be fearful of the night.” 

John Brashear’s 75th birthday party, November 24, 1915.

Credit: AIP Emilio Segrè Visual Archives, Catalog ID: Brashear John E1

Brashear lenses were used in many influential experiments and telescopes and his method for silvering mirrors became standard. His lenses were employed at the Allegheny Observatory where Samuel Langley made groundbreaking solar observations and John Keeler discovered that Saturn’s rings are not solid. They were used in spectrographs at Lick, Princeton, and Yerkes observatories. Michelson continued to use Brashear lenses in his high precision light measurements, including his measurement of the wavelength of cadmium red radiation that was used to define a standard meter. Brashear lenses are what we thought mantis shrimp eyes could be: a tool to see light and color differently. Through Brashear’s lenses we gained a new perspective on the universe.

Left image: 1914 image of the Thaw Memorial Refractor, its mirror was built by Brashear Lens Co.

Right image: I took this photo of the same telescope which we used for astronomy coursework in 2021. In 1985, the lens was replaced. If you zoom in very closely, you can see a bright pixel in the sky just below the end of the telescope. That pixel is Mars, the planet we were photographing that evening!

 

As an undergraduate student at the University of Pittsburgh, I conducted astronomy research out of the Allegheny Observatory. John Brashear is the de facto patron saint of the observatory and his presence is felt in the building and through the observatory’s mission: keeping astronomy free to the public. Normally, I am cautious about becoming attached to historical figures, but in John I am reminded why I love astronomy. Nothing makes me feel more connected to humanity than looking out into space and marveling at its beautiful secrets. John Brashear believed that every person deserves access to the stars and dedicated his life to making that possible. Now buried in the crypt of the Allegheny Observatory, his legacy holds true. 

Bonus John Brashear stories:

In Phoebe’s last years, she was unable to walk so she and John rented a lake house and a small sailboat. He taught himself to sail and rigged the boat to comfortably accommodate Phoebe. At night, he brought her out into the middle of the lake so they could gaze at their beloved stars. Though he was busy fundraising for the Allegheny Observatory, he never let work get in the way of spending time with her. Neighbors remarked that Phoebe was not particularly beautiful, but from the way John looked at her you would think she was the most beautiful woman to have ever lived. 

While John was saving up to buy a boat, his friend bought one for him, “not for charity but as a recognition of a life work so often done without monetary compensation.”  While working on the lake, he frequently made stops in town and ran errands for his neighbors. Unfortunately, the lake was fire--prone and one day his boat burned down. Andrew Carnegie heard of this and bought John and Phoebe a new boat, the nicest on the lake. Ten years later that boat burned down as well, so the community pooled their money together and bought him another one as thanks for his constant help. 

One year on the lake there was a bad forest fire that sent all kinds of animals, from raccoons to possums, to deer, fleeing to the lake for refuge. Many of the animals drowned and washed ashore in the following weeks. John carried animals one by one to a nearby hill and buried them there on what he called “Cemetery Hill”. 

A stained glass in the Allegheny Observatory depicting Urania the Greek muse of astronomy holding the celestial sphere. She is lifting her hand to the Pleiades and Hyades star clusters. Beside her in the foreground is the lamp of knowledge and in the background is the Acropolis. Below her is a rainbow of light split into its component colors representing the advancements in spectroscopy. 

You can listen to Initial Conditions: A Physics History Podcast wherever you get your podcasts. A new episode will be released every Thursday so be sure to subscribe! On our website, you will find transcripts, show notes, and our suggested resources to learn more about each topic we discuss. 

Brashear, John A. John A. Brashear; the autobiography of a man who loved the stars, edited by W. Lucien Scaife. New York: The American society of mechanical engineers, 1924.

Gaul, Harriet A., and Ruby Eiseman. John Alfred Brashear, scientist and humanitarian, 1840-1920. Philadelphia : University of Pennsylvania press, 1940.

Livingston, Dorothy Michelson. The master of light; a biography of Albert A. Michelson. New York: Scribner, 1973.

Michelson, Albert A., and Edward W. Morley. “On the Relative Motion of the Earth and the Luminiferous Aether.” American Journal of Science 34, no. 203 (1887): 333-345.

“Spectroscopy and the Birth of Astrophysics.” Tools of Cosmology. American Institute of Physics. Date Accessed August 31, 2022.  https://history.aip.org/exhibits/cosmology/tools/tools-spectroscopy.htm