Atomic Clock

 By Bruce Shawkey

Found this article about an satomic clock that was on exhibit at a Brussels fair in 1958. It weighed several thousand pounds and was the size of a commercial refrigerator. It's amazing to think that a quartz watch weighing as little as 10 grams can achieve an accuracy that satisfies the accuracy most people require.

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The atomic clock, which is being shown at the Brussels Fair, is the result of brilliant and patient research work undertaken by the Laboratory of Horological Research at Neuchatel and the Institute of Physics. it is due to the tenacious work of four scientists, Mssrs. Bouanomi and Hermann assisted by Mssrs. Kartaschoff and De Prins, that this marvel of precision has been made ready in time to show the world this new remarkable feat of Swiss technique. 

One of the outstanding exhibits at the Brussels Fair this year is the Atomic Cluck built in the research laboratories of Neuchatel. Switzerland, and which has a margin of error of 100-thousandths of a second per day. 

Until recently, the fundamental unit of time was the second of mean solar time based on the rotation of the earth about its axis and defined as 1/86,400 of a mean solar day. It was found from astronomical observation that the period of rotation of the earth is not strictly constant and therefore that mean solar time is not a measure of uniform time. And so although mean solar time remains in common use, it has been necessary for scientific purposes to find a uniform scale of time.

With improved technical knowledge, scientists invented the quartz clock that kept better time than the earth for short lengths of time but lacked absolute precision over intervals of several years. The last timepiece to come into being is the atomic clock. The first of these was built ten years ago in the U.S.A. and today several such clocks function with great precision in that country as well as in Great Britain and Switzerland.

The operating of the Neuchatel Clock is as follows:

 In a cylinder in which a pumping system maintains a high rate of vacuum, a jet of ammonia molecules produces oscillations in the cylinder while radio waves are being given off. The frequency of these waves is the same as that of the molecules -- that is to say about 24 billions to the second. The device which produces radio waves by means of molecules is called a molecular oscillator. The radio signal is amplified in a receiving instrument and used for the exact timing of the quartz clock.

The Atomic clock therefore comprises two parts: the atomic oscillator and the quartz clock. The molecular oscillator is the regulator that subdivides time into short equal intervals. The quartz clock is the medium that counts the number of intervals and indicates the time. Since the quartz clock in itself is a very highly accurate timekeeper, it is not necessary for the molecular oscillator to function all the time and it need only be operated once a week to check the quartz clock.

Since the precision of an atomic clock can be measured only by comparing it with another clock of the same type, the instrument has been provided with two molecular oscillators. The measured precision of the one compared to the other is about one hundred thousandths of a second per day.