CLOCKING THE SPEED OF LIGHT

Midshipman Albert A. Michelson excelled in science during his years at the Naval Academy.  In his 29-member graduating class of 1873 he was ranked ninth overall, first in the subject of optics and second in thermodynamics.  He ranked only 25th in seamanship however, neither did he excel on his obligatory Passed Midshipmen cruises the following year.  But Michelson’s academic genius did not go unrecognized for LCDR William T. Sampson, Head of the Department of Natural and Experimental Philosophy, brought ENS Michelson back to the Academy in December 1875 to teach physics and chemistry.

Over the subsequent years Michelson became interested in the vexing problem of measuring the speed of light, a controversial topic to physicists of that day.  Capitalizing on the work of French physicist Jean Bernard Leon Foucault, Michelson designed an apparatus to bounce a light beam between a rotating mirror and a stationary mirror 500 feet apart.  His crude setup, constructed mostly of spare parts scrounged from Academy labs, was substantially more precise than Foucault’s, and during the Summer of 1878 he improved on the accuracy of the Frenchman’s estimates.

Still not satisfied, in the Spring of 1879 he expanded his setup using a straight line of sight along a 2000-foot seawall at the Academy.  His rotating mirror was mounted at one end of the seawall near what was then the ferry pier (currently the entrance to MacDonough Hall) and a plane mirror was placed behind what is today Maury Hall.  Of necessity, Michelson also developed a novel method to accurately calibrate the speed of his rotating mirror with a tuning fork.  Using this more accurate setup Michelson clocked the speed of light at 186,355 miles/second.  This he dutifully reported to the Secretary of the Navy on this day in his letter, “Experimental Determination of the Velocity of Light.”  Still not satisfied, Michelson further refined his setup in the years that followed, mounting mirrors at Ft. Myers that shot beams of light across the Potomac River to the Naval Observatory and the Washington Monument.

Michelson resigned his commission in 1882 and in later years further expanded his reputation in the international scientific community.  His decades of hard work and intellectual brilliance were honored in 1907 with the awarding of the Nobel Prize for physics–the first American scientist to receive this award.  The seawall along which his famous experiments were conducted has since been demolished.  But today a marker on the plaza between Michelson Hall and Chauvenet Hall at the Academy identifies Michelson’s line of sight along the former seawall of 1879.

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CAPT James Bloom, Ret. 

Jaffe, Bernard.  Michelson and the Speed of Light:  Biography of a Scientist.  Garden City, NY: Anchor Books, 1960, pp. 50-56.

Livingston, Dorothy Michelson.  The Master of Light:  A Biography of Albert A. Michelson.  New York, NY: Charles Scribner’s Sons, 1973, pp. 35-66, 232-37.

McAllister, D.T.  Albert Abraham Michelson:  The Man Who Taught the World to Measure (Michelson Museum Pub. No. 3).  China Lake, CA: Technical Information Department, Naval Weapons Station China Lake, May 1970.

Wilson, John H., Jr.  Albert A. Michelson:  America’s First Nobel Prize Physicist.  New York, NY: Julian Messmer, Inc., 1958, pp. 62-73.

ADDITIONAL NOTES:  Michelson’s apparatus projected light onto a plane mirror spinning at 128 rotations/second.  The light was reflected off this mirror along the seawall to strike the distant second mirror.  From here it was reflected directly back along the seawall to the original rotating mirror.  During the time it took the light to travel down the seawall and back, the first mirror had rotated a few degrees further, reflecting the returning light beam back to Michelson at a slight angle.  The measure of this angle and the known speed of the mirror’s rotation were used to calculate the time it took for the light to travel down and back along the 2000-foot seawall.  The accuracy of Michelson’s calculation of 186,355 +/- 31 miles/second has withstood the test of time and further experimentation.  Michelson’s Nobel Prize included the sum of 139,000 Swedish Crowns, approximately $40,000.

Though his first love was science, Michelson never lost his affinity for the Navy.  After resigning his commission in 1882 he continued for years in the Naval Reserve.  Between 21 June 1918 and 8 March 1919 Michelson voluntarily returned to active duty while America fought in WWI.  He was assigned to the Navy Bureau of Ordnance as a consultant working on the practical problems of gunnery range finding and on engineering a substitute for high-quality German optical glass.  Michelson moved to Pasadena, CA, in his later years, where he died in 1931.  Michelson Laboratory on the Naval Weapons Center China Lake is named in his honor, as is the oceanographic ship USNS MICHELSON (T-AGS-23).

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