Marine timekeeper, H2. Made between 1737 and 1739, this is a larger and more solidly built version of H1, with the additional refinement of a remontoir - a device to ensure that the drive to the two balances is as uniform as possible. It is probable that Harrison, who had moved to London by this time, had some help in making parts of H2. Because he discovered a design fault with its balances, Harrison never allowed H2 to be tested at sea. He kept it running at his house for many years until, in 1766, it was taken from him by the Astronomer Royal under the conditions of the longitude prize.