My vigilance went unrewarded. I had closed the window to exclude the yellow mist, but subconsciously I was aware of its encircling presence, walling me in, and now I found myself in such a silence as I had known in deserts but could scarce have deemed possible in fog-bound London, in the heart of the world's metropolis, with the traffic of the Strand below me upon one side and the restless life of the river upon the other.