I visited the recently refurbished Royal Observatory at Greenwich last weekend, where there is, inevitably, a whole section devoted to Harrison and his clock-based solution to the ‘longitude problem’. (The story of his fight with the Astronomer Royal, Neville Maskelyne, and the astronomy establishment, which preferred the so-called ‘lunar solution’, is famously told by Dava Sobel in her book ‘Longitude’.) But the reason for posting is that the Observatory describes Harrison’s fourth clock, the H-4 pocket watch, as “one of the most important machines ever made”.

The case can be made fairly easily; without being able to calculate longitude accurately, the seas are inherently unsafe, no matter how good your maps are. Harrison’s clock, especially as the price came down through widespread production, enabled the huge global expansion of trade which we saw in the 19th century. In an era in which globalisation, and its limits, are once more on our minds, the technology of global trade is more visible to us.

But I wondered if this was a widespread view. As it happens, in 1998 John Brockman asked the high-powered mailing list to his Edge website ‘what is the most important invention in the past 2,000 years?’ (not quite the same question, but I think close enough). I’m not going to round up the answers here, but Gutenberg’s printing press does well, along with electricity, the computer, the gun, the number system, and the technology needed to domesticate the horse. (Brockman edited the replied into a book, The Greatest Inventions, and there was press coverage, if you want to know more). Harrison’s clock isn’t mentioned.