The first of Harrison’s series of five sea-clocks (chronometers) was completed in 1735. Commonly referred to as H.I (Harrison’s No. I) the key advance in H.I was that instead of a pendulum it had a balance spring with two 5-lb weights connected by brass arcs. This meant that if it was tilted or turned, as by the movement of the sea, the "regularity of the balances" was not disturbed and moreover, any "particular movement communicated to one balance will be automatically counteracted by an equal and opposite movement of its opposing counterpart." (Quill, 1966:41). The chronometer weighed 72 pounds and was subjected to extensive trials on a barge on the Humber. These were judged so successful that later in 1735 the Board of Longitude was approached again. They agreed to a sea-trial. Hence in 1736 H.I sailed to Lisbon. Details of this trip are only scarce although it is apparent that H.I was once again relatively successful losing only three seconds in 24 hours. However, Harrison decided that H.I could not be further improved and abandoned working with it turning his attention instead to the design and manufacture of H.2. (Quill, 1966:47).
