Signedunsigned
Inscribedon the pedestal: CRUFT LABORATORY
FunctionThis mirror was part of a larger experimental set-up devised by Wilmer C.
Anderson to measure the speed of light. According to the description in the Review of Scientific Instruments, the set-up consisted of a light source (a 500-Watt Point-O-Lite bulb), Nicol prisms, a Kerr cell (a photoelectric cell that replaced the human eye; it is really the innovation here), and mirrors. The present mirror, from Anderson's description, could be the one he identified as M5.
In the same article, Anderson said that after a series of 651 measurements, the mean result for the speed of light was 299,765 km/s ± 15 km/s. Two years later, he was able to get an even more precise number using 2895 observations: 299,776 km/s ± 14 km/s.
The origins of Anderson's work is found in his Ph.D. dissertation at Harvard University, completed in 1936 and entitled A High-Frequency Method for Measuring the Velocity of Light.
Primary SourcesWilmer C. Anderson, "A Measurement of the Velocity of Light," Review of Scientific Instruments 8 (1937): 239-247.
Wilmer C. Anderson, "Final Measurements of the Velocity of Light," Journal of the Optical Society of America 31 (1941): 187-197.
Time, 27 March 1939 (online here.)
"Light Measured by Harvard Device; Meter Records Speed With Least Error Ever Known," New York Times, March 17, 1939, 19.
ProvenanceFrom the Department of Physics, Harvard University.