But steamships didn't lose their sails until the 1880s, because early marine engines had a nasty habit of breaking down.

Until ships became large enough (and engines small enough) to mount two engines side by side, they needed to keep sails.

It's clear that petrol-driven engines have no future.

His main thesis is that the buzz of urban life, and the opportunities it offers for co-operation and collaboration, is what attracts people to the city, which in turn makes cities into the engines of art, commerce, science and progress.