Geology Reference
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friend Bob Lawson, whose mathematical ability Holmes still
relied upon. A touching acknowledgement at the end of the
book reveals the depth of their friendship:
Doctor Lawson and I have frequently collaborated during
the last two decades, and the development of the subject owes
more to his influence than his published contributions can
indicate. Throughout the writing of this . . . I have had the
great advantage of constant discussion with him. His experi-
ence as an investigator of radioactive phenomena has been
freely placed at my disposal and my indebtedness to him is
greater than can be formally expressed.
Even today we can feel the tremendous warmth and respect
that existed between these two men.
Another, more conventional acknowledgement was to Dr
Francis William Aston for providing Holmes with data on lead
Back in 1910 Aston had been working at the Cavendish
Laboratory in Cambridge. Like all the others there at that time
he too had been carried along with the excitement of radio-
activity and the new theories emerging about the atom. Thus
when isotopes were discovered Aston helped develop the first
mass spectrograph, forerunner of the mass spectrometer, an
apparatus which separates isotopes according to their atomic
weights by passing them through a magnetic field. Development
of the mass spectrometer was to revolutionise dating methods.
Today it is a highly sophisticated instrument that can analyse a
sample for its uranium and lead isotopes (or almost any element
you care to think of) in a few minutes, and tiny mass spec-
trometers are put on the Moon and Mars probes to test the
composition of the atmosphere and the soil, giving almost
instantaneous readings. But in Aston's day they were unwieldy,
hand-built instruments requiring constant care and attention.
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