After innumerable experiments Harrison at length composed a frame somewhat resembling a gridiron, in which the alternate bars were of steel and of brass, and so arranged that those which expanded the most were counteracted by those which expanded the least.

By this means the pendulum contained the power of equalising its own action, and the centre of oscillation continued at the same absolute distance from the point of suspension through all the variations of heat and cold during the year.[5] Thus by the year 1726, when he was only thirty-three years old, Harrison had furnished himself with two compensation clocks, in which all the irregularities to which these machines were subject, were either removed or so happily balanced, one metal against the other, that the two clocks kept time together in different parts of his house, without the variation of more than a single second in the month.

One of them, indeed, which he kept by him for his own use, and constantly compared with a fixed star, did not vary so much as one whole minute during the ten years that he continued in the country after finishing the machine.[6] Living, as he did, not far from the sea, Harrison next endeavoured to arrange his timekeeper for purposes of navigation.
He tried his clock in a vessel belonging to Barton-on-Humber; but his compensating pendulum could there be of comparatively little use; for it was liable to be tossed hither or thither by the sudden motions of the ship.

He found it necessary, therefore, to mount a chronometer, or portable timekeeper, which might be taken from place to place, and subjected to the violent and irregular motion of a ship at sea, without affecting its rate of going.

It was evident to him that the first mover must be changed from a weight and pendulum to a spring wound up and a compensating balance.
He now applied his genius in this direction.