An Hourglass of Great Precision - Four Revolutions in the Earth Sciences - page 35

sumptions. At various times, he accepted radioactivity, denied it, and, finally, ig-
nored it.
According toRutherford'sbiographer,Kelvin agreed toabetthat hewouldsoon
accept the new radioactivity. At the subsequent meeting of the British Association
in 1904, Kelvin paid off. 9 He may have honored the bet, but his published state-
ments took the opposite tack. In a series of letters to the London Times in 1906,
asserting that he had spent “more hours in reading the first and second editions of
Rutherford's Radio-activity” than almost any other person, Kelvin denied that ra-
dium could emit heat in perpetuity or account for the Earth's heat. As for the heat
of the Sun, that was attributable not to radioactivity but, as he had long said, to the
release of gravitational energy. Kelvin claimed that radium is not a chemical ele-
ment but a molecular compound composed of lead and five helium atoms. 10
In one of the last papers of his life, Kelvin wrote that the heat emitted by radium
isnotcausedbyalphaparticlesbutbyelectrons,whichsomehowbecome“loaded”
with energy. This process, he said, can “go on forever, without violating the law of
conservation of energy, and without any monstrous or infinite store of potential en-
ergy in the loaded Radium atom.” 11 Having begun his attack on geology in order
to refute Lyell's claim that the Earth is a perpetual-motion machine, Kelvin now
made a rather similar claim himself.
Lord Kelvin died in 1907, the same year the statement above appeared, four
months after attending yet another meeting of the British Association, where ac-
cording to Rutherford he had taken part in a lively discussion on the “Constitution
of the Atom.” 12 Though in the end Kelvin turned out to be wrong about the age of
the Earth and the solar system, his insistence on quantitative methods and that the
Earth's age measured not in the few thousand years the Bible allowed but at least
in a score or more million years helped propel geology into a new century.