"On Saturday, May 13th, 1826, I went to London on the way to Dolcoath,
and received four chronometers from the Royal Observatory,
Greenwich. I travelled by Devonport and Falmouth to Camborne, where I
arrived on May 20th and dined at the count-house dinner at the mine. I
was accompanied by Ibbotson, who was engaged as a pupil, and intended
for an engineer. On May 24th Whewell arrived, and we took a pendulum
and clock down, and on the 30th commenced the observation of
coincidences in earnest. This work, with the changing of the
pendulums, and sundry short expeditions, occupied nearly three
weeks. We had continued the computation of our observations at every
possible interval. It is to be understood that we had one detached
pendulum swinging in front of a clock pendulum above, and another
similarly mounted below; and that the clocks were compared by
chronometers compared above, carried down and compared, compared
before leaving, and brought up and compared. The upper and lower
pendulums had been interchanged. It was found now that the reliance
on the steadiness of the chronometers was too great; and a new method
was devised, in which for each series the chronometers should make
four journeys and have four comparisons above and two below.
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