Harrison's second timekeeper, H2, has been in the horology conservation workshop at the Royal Observatory undergoing research for quite a few weeks now and its study is proving most interesting. The complete measurement of all the parts has now been completed and photography is well under way.

West Dean College have been extremely helpful in making their XRF metals analysis equipment available to us, and the Clock Course Tutor, my old colleague Matthew Read, came up to Greenwich for the day to help with tests on a number of parts of H2 which appear to employ unusual alloys.

Some years ago the V&A kindly carried out XRF analysis on some of the parts of H3 and we discovered that Harrison employed various types of tin-bronze, principally in place of steel, which naturally would have been inclined to rust in a marine environment. It is reassuring to find after this recent analysis that those results were confirmed by the same alloys, chiefly a low tin-bronze where good tensile strength is required, and a very high tin-bronze where high compression strength is needed (such as in the anti-friction segments supporting the balances).

As is now well known, these timekeepers run without lubrication, and I was most interested to see if H2, like H1, has survived in good order after 50 years of constant running. I calculated, for example, that the balances, which each weigh over 8lbs, will have rolled on their bronze segments over one and a half billion times! Well, I was astonished to find that, after all those years, the bearings are simply unmarked. I am sure the balances could continue for several more billion oscillations without harm coming to them.

Delays over the photography have meant that the timekeeper's return to the gallery has also been delayed, but reassembly is now about to start. Further updates will follow before the timekeeper returns to exhibition in the Longitude Gallery, now estimated to be sometime in early August.