R: A.A. Michelson's 1879 Determinations of the Speed of Light

michelson_1879 {loon.data}

R Documentation

A.A. Michelson's 1879 Determinations of the Speed of Light

Description

In 1879, Albert Abraham Michelson conducted an experimental study to determine the speed of light using a rotating mirror apparatus at the U.S. Naval Academy in Annapolis, Maryland in 1879.

Details on the apparatus, the optical theory, and the conduct of the experiment are given in the reference. An abbreviated summary of these follows the variable descriptions.

Format

A data frame with 100 rows and 15 variables

Speed: The determined speed of light in air in kilometres per second.
Beat: Number of beats per second between tuning forks.
Correction: Correction for temperature to a standard fork in beats per second.
Day: Day of experiment in progress (June 5 is day 1) on which these measurements were taken.
Difference: Difference betweeen the greatest and least values of revolutions.
Quality: Subjective measure of the quality of the image 'I'; the more distinct was the image the higher the quality (1 = poor, 3 = good).
Displacement: Displacement of image 'I' from slit 'S' in divisions of the micrometer.
Image: Micrometer position of the deflected image.
Radius: Radius of measurement in feet.
Revolutions: Number of times the mirror revolved per second.
Screw: Measure of one screw turn in millimetres.
Slit: Micrometer position of the slit providing the light source 'S'.
Temperature: Air temperature measured in degrees Fahrenheit.
Time.of.day: Time of day at which the observation was recorded. 'AM' means one hour after sunrise and 'PM' one hour before sunset.
Remarks: Unusual remarks recorded for that observation.

Details

The experiment is conducted within a closed and darkened small building at the U.S. Naval Academy. Light enters the building from one corner passing through a slit 'S' whose location is precisely determined using a micrometer.

The light then proceeds to hit a rotating mirror at the other end of the building's interior from whence it is reflected out of the building through an opening in a corner different from that of the source.

The light beam travels outside to strike another (stationary) mirror which reflects it back into the building through the same corner it exited whereupon it then strikes the rotating mirror.

Depending on the position of the rotating mirror, the returning light will be reflected off it to land at some position 'I' near the original source given by the slit 'S'.

The speed of the rotating mirror is controlled using an adjustable pump to blow air across a surface to rotate it. If the speed of rotation is just right, a crisp image 'I' of the reflected slit will appear near the original source 'S'. The speed is adjusted until this is the case.

The speed of rotation is determined using an electric tuning fork connected to the rotating mirror and whose frequency was measured by comparing it to a second standard tunig fork of known frequency. The electronic fork frequency was compared to the standard fork by determining the number of beats per second difference the two (by counting over 60 seconds).

With a speed of revolution and the displacement measured between 'S' and its returned image 'I', a measurement of the speed of light could be had.

See reference for more details.

Author(s)

R.W. Oldford

References