John Harrison, the man who eventually solved longitude at sea with a clock, started out as a carpenter, and his first clocks were made mostly of wood. That sounds like a beginner’s compromise, but it took him somewhere. The oils of his day were the weak point of any clock: they thickened in the cold, thinned in the heat and slowly went gummy, and a clock is only as steady as the friction inside it. So instead of hunting for a better oil, Harrison kept finding ways to need less of it, with parts made of lignum vitae, a tropical wood so resinous it greases itself, and later with movements designed to run on almost none at all. A turret clock he built in the early 1720s for the stables at Brocklesby Park, in Lincolnshire, is reported to be still going. The usual move, when one part of a machine keeps failing, is to make that part better. His was to keep asking whether the machine had to have it.