plane mirror on stand
Date: 1937-1939
Inventory Number: 1996-1-0680
Classification: Mirror
Maker: Wilmer C. Anderson
User: Department of Physics, Harvard University (founded 1884)
Cultural Region:
Place of Origin:
Dimensions:
32 × 31 × 31 cm (12 5/8 × 12 3/16 × 12 3/16 in.)
Description:
This eight-inch mirror is mounted on a heavy stand, which has three feet and leveling screws. The mirror is supported by two columns and a circular base. It can rotate sideways using two horizontal screws that finely move a vertical pin centered between them. When in use, the mirror is inclined forward and set in a clamp. The clamp is formed by two screws, again to allow a fine up-and-down motion of the mirror. These fine motions were to better target the reflection of the light beam used in the experiment.
In Collection(s)
Signedunsigned
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, was probably the one he identified as M2 or M3.
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.
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, was probably the one he identified as M2 or M3.
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.
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.
