Higher Beauties: The Discovery of the Speed of Light in the San Gabriels

Mount Wilson Observatory at sunset. | Screenshot from UCLA Mount Wilson Cam
I always think of Michelson as the artist in Science. His greatest joy seemed to come from the beauty of the experiment itself, and the elegance of the method used...
--Albert Einstein, on the centennial of Albert Michelson's birth, 1952

The interplay between art and science was always complementary in the life of American physicist Albert Michelson. A talented painter since his days as a cadet midshipman in the U.S. Navy, Dr. Michelson held a deep fascination in both the aesthetic and physical properties of light. He excelled in the field of optics at the U.S. Naval Academy, and was particularly engrossed in the challenges of measuring the speed of light. He ultimately chose to pursue a career in science over art when he graduated in 1873. "The aesthetic side of the subject is, I confess, by no means the least attractive to me," he asserted about the artistic appreciation of light in a lecture at the Lowell Institute in 1899. He was more compelled, however, to seize light through the faculties of reason, not the senses, to "perceive the still higher beauties which appeal to the mind."

Michelson's decision to pursue the "higher beauties," as he referred to the laws of Nature, led him into the San Gabriel Mountains to perform one of the most famous scientific experiments in human history.

 From left to right: Dr. Albert Michelson, Dr. Albert Einstein, and Dr. Robert A. Millikan, President of the California Institute of Technology, at the California Institute of Technology in the 1920s or 1930s | Photo Courtesy of the Los Angeles Public Library

During his career, Michelson had developed optical precision instruments to discover the effect of the Earth's motion on the observed velocity, and to show that light travels at a constant speed in all inertial systems of reference. His instruments and investigations had earned him the Nobel Prize in physics in 1907, becoming the first American scientist to receive the coveted award.

In 1922, Michelson was determined to best the previous 44 years of his life he had spent attempting to calculate the velocity of light. His goal was to arrive at a measurement with no more than a possible 0.001% error. This definitive measurement, he believed, could be attained with the plotting of an elegant yet daunting plan: a beam of light would be launched from a station at the Mount Wilson Observatory, travel 22 miles to a station containing a return mirror on a ridge of Mount San Antonio, called Lookout Mountain, and re-traverse its way back to Mount Wilson. The return beam would hit a rotating mirror driven by compressed air, and by measuring the minute change in angle of the mirror during a round trip, the speed of light could be measured.

Arrangement of Michelson's light experiment between Mount Wilson and Lookout Mountain near Mount San Antonio | Source: "Measurement of the Velocity of Light Between Mount Wilson and Mount San Antonio"

Michelson's Lookout Mountain station | Source: Otherhand.org

Lookout Mountain today, showing the remaining concrete piers of the station. | Photo: Daniel Medina

In order to ensure the accuracy of the experiment between Mount Wilson and Lookout Mountain, the exact distance between the two peaks had to be verified. Since the rough mountainous terrains made it difficult to obtain an accurate reading, the U.S. Coast and Geodetic Survey stepped in to triangulate the distance from a base line they developed at the base of the foothills in the San Gabriel Valley. When it was completed, it was reported in the Survey's "A Geodetic Measurement of Unusually High Accuracy," that the error of the line between the two peaks was approximately 1 in 5,000,000." The report added, "It is believed that the length of this line has been determined with greater accuracy than that of any line of triangulation in this or any other county." Emboldened with such precision, the experiment was ready to commence in 1924.

Diagram of the Michelson triangulation | Source: "A Geodetic Measurement of Unusually High Accuracy"

 Measuring the base line. | Source: "A Geodetic Measurement of Unusually High Accuracy"

The base line is measured to pass through the window in each end of a house. | Source: "A Geodetic Measurement of Unusually High Accuracy"

For the next two years, Michelson conducted his unprecedented experiments, alternating sizes and rotational speeds of the mirror on Mount Wilson. Each time, the beam of light would dash its 44-mile round trip course in far less than the blink of an eye.

Fortunately, for the then-73-year old Michelson, his great experiment in the San Gabriels worked. After compiling his data, he found that the final result of the speed of light, as published in the Astrophysical Journal in 1927, was 299,796 km per second. Modern measurements of light speed in a vacuum is 299,792 km per second; the calculations from the Mount Wilson-Lookout Mountain experiment were astonishingly accurate for its day.

Michelson became the first person to accurately measure the speed of light, the critical value "c" in Einstein's energy matter equation "E = mc2" that would pave the way for the development of the revolutionary Theory of Relativity. This universal constant proved so crucial that Einstein reiterated at an address at Caltech in 1931, "Without your work this theory would today be scarcely more than an interesting speculation."

Following his breakthrough, Albert Michelson had only a brief tenure left on earth to enjoy the accolades and acclaim that rained down on him. He died in 1931, the same year his watercolors of California landscapes were exhibited at the Pasadena Art Institute. There is little doubt that he must have cherished this particular honor that came from outside of the realm of physics. His legacy was now affixed to both the arts and sciences, a final demonstration of his reverence for the intricate wonders of light.

A geographic marker on the remains of a concrete pier on Lookout Mountain points to the summit of Mount Wilson | Photo: Daniel Medina

Shards of glass from the Lookout Mountain station are scattered over parts of the summit. | Photo: Daniel Medina

Remains of concrete piers on Lookout Mountain | Photo: Daniel Medina

A sign marks the summit of Lookout Mountain | Photo: Daniel Medina

About the Author

I grew up in the San Gabriel Valley and enjoy exploring Los Angeles and learning about its origins.
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