85 days and begot Radium A, which lived 3 minutes and
begot Radium B, which lived 26.8 minutes and begot Radium C, which lived
19.5 minutes and begot Radium D, which lived 12 years and begot Radium
E, which lived 5 days and begot Polonium, which lived 136 days and begot
Lead.
The figures I have given are the times when half the parent substance
has gone over into the next generation. It will be seen that the chemist
is even more liberal in his allowance of longevity than was Moses with
the patriarchs. It appears from the above that half of the radium in any
given specimen will be transformed in about 2000 years. Half of what is
left will disappear in the next 2000 years, half of that in the next
2000 and so on. The reader can figure out for himself when it will all
be gone. He will then have the answer to the old Eleatic conundrum of
when Achilles will overtake the tortoise. But we may say that after
100,000 years there would not be left any radium worth mentioning, or in
other words practically all the radium now in existence is younger than
the human race.
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