It's nice to see that John Harrison is finally getting acknowledgement with the dedication of a stone to his memory in Westminster.  He made the first clock to keep accurate time on shipboard and thus solved the problem of how to measure longitude.  His story, and the way his solution was ignored by the scientific establishment was wonderfully told by Dava Sobel.  He was a carpenter, not a member of the scientific establishment.  He thought about the problem in a different way, in a time (sic) where the concept of time itself was distant from our current understanding.  His various clocks can be seen at the Greenwich Maritime Museum in London and its worth the trip down to see it (the best approach being via the Thames from Westminster Pier.