Moving Clock Found to Run Slower Than Stationary One

From Horology magazine, October 1938

Moving Clock Found to Run Slower Than Stationary One

Bell Laboratories Scientist Confirms 40-Year-Old Theory


A famous theory of science, announced forty years ago, has at last been confirmed by experiments in the Bell Telephone Laboratories, according to a paper presented by Dr. Herbert E. Ives before a meeting of the National Academy of Sciences in Washington recently. Dr. Ives has shown that a moving clock actually does run slower than one at rest.


So slight is the slowing down that no speeds available to experimenters when the theory was announced were adequate for a crucial test. But by using as a "clock" the light-giving oscillation of a hydrogen ion,which can be shot down a vacuum tube at a thousand miles a second, it is possible to measure a definite change in the color of the light. That, of course, means a change in the rate of vibration of the atom.


Dr. Ives' apparatus uses a vacuum tube in which there is a small amount of hydrogen. An electric arc breaks down the hydrogen molecules into charged ions.


These are picked up by a high-voltage electric field and brought up to speeds of the order of a thousand miles a second. Looking into the end of the tube, the observer sees these ions approaching him, and by means of a mirror he also sees them apparently receding from him.

If his eyes were sufficiently sensitive to color, he would notice that the receding ones were redder than the approaching ones; this is the Doppler effect, which also makes the horn of an approaching car sound higher pitched than that of a receding car. But as compared with the color of stationary ions, those moving in either direction are redder; that is, they vibrate more slowly. And that is what Fitzgerald, Larmor and Lorentz proposed nearly 40 years ago-atomic "clocks" oscillating more slowly as they move through a stationary medium called "the ether."