John Harrison and his brother James were introduced to clock repair by their father, Henry. Clock making, or horology, was undergoing a developmental revolution. Mechanical clocks had existed since the fourteenth century. They remained rather primitive in their operation until Christiaan Huygens invented the weight-and-pendulum clock in 1656.

Self-taught individuals, John and James were also introduced to carpentry and surveying by their father. They chose, however, to become totally involved in making clocks, and almost immediately began developing their own improvements to them. One such innovation was the gridiron pendulum, which consisted of a grid of iron and brass that compensated for changes in temperature.

Perhaps the major problem with clocks in those days was that they were totally dependent upon the earth's gravity for their operation. This meant that they could not keep accurate time at sea, and could not be adapted for portability. Even moving them across...