He invented a curious monochord, which was
not less accurate than his clocks in the mensuration of time.
His ear was distressed by the ringing of bells out of tune, and
he set himself to remedy them. At the parish church of Hull, for
instance, the bells were harsh and disagreeable, and by the
authority of the vicar and churchwardens he was allowed to put
them into a state of exact tune, so that they proved entirely
melodious.
But the great work of his life was his marine chronometer. He
found it necessary, in the first place, to alter the first mover
of his clock to a spring wound up, so that the regularity of the
motion might be derived from the vibrations of balances, instead
of those of a pendulum as in a standing clock. Mr. Folkes,
President of the Royal Society, when presenting the gold medal to
Harrison in 1749, thus describes the arrangement of his new
machine. The details were obtained from Harrison himself, who
was present. He had made use of two balances situated in the
same plane, but vibrating in contrary directions, so that the one
of these being either way assisted by the tossing of the ship,
the other might constantly be just so much impeded by it at the
same time. As the equality of the times of the vibrations of the
balance of a pocket-watch is in a great measure owing to the
spiral spring that lies under it, so the same was here performed
by the like elasticity of four cylindrical springs or worms,
applied near the upper and lower extremities of the two balances
above described.
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