[time-nuts] Lifetime of Cesium tube

Tom Van Baak tvb at leapsecond.com
Thu May 12 21:46:46 EDT 2005

> Molecule: A unit of matter, the smallest portion of an *element* or
> compound that retains chemical identity with the substance in mass.

I don't know about an official chemistry definition
but in the context of timekeeping and clocks, you
will see the term molecule used only in the case
of ammonia; the first atomic clock in 1949; where
it is sometimes, correctly so, called a "molecular

The rest of the clocks -- the ones based on hydrogen,
cesium, rubidium, etc. -- are called atomic clocks
and the happy bits of matter that fly around are called
atoms, by both technical literature and popular press.

A good example of the proper use of the terms
molecular and atomic in the context of clocks is:


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