Paris is called the City of Light, possibly because of its early adoption of gas street lighting. But that would not explain why, as I approach Gare du Nord on Eurostar during daytime, I experience a soft dazzle, similar to when I see a pebbly beach. This is not a meteorological phenomenon; the weather in Paris is only slightly better than London’s. Instead, the luminosity owes something to the buff or light-grey limestone of the older buildings (including the Sacré Coeur, rearing like a great ghost to my right), its pallor perpetuated by the whitewashed exteriors of newer buildings.