"Even the Thames, running its sluggish course beyond the line of the trees behind us, smells fresh here, so far to the west of London."
is a large river that flows through London. During this period the expansion of world trade saw many new dockyards built on the Thames, and the river filled with ships. The Thames was also used for public transportation, with boats of all kinds ferrying passengers to and fro. During this time there was very little organised waste disposal in the city, and raw sewage was thrown into the streets and the river. The Thames would have been incredibly dirty and disease-ridden.