Throughout the story, the narrator uses metaphor to compare the crowded London streets to an ocean:
As the darkness came on, the throng momently increased: and, by the time the lamps were well lighted, two dense and continuous tides of population were rushing past the door. At this particular period of the evening I had never before been in a similar situation, and the tumultuous sea of human heads filled me, therefore, with a delicious novelty of emotion. I gave up, at length, all care of things within the hotel, and became absorbed in contemplation of the scene without.
By using phrases like “tides of population,” “rushing,” and “tumultuous seas of human heads,” the narrator draws parallels between the thronging London crowds and the waves of the sea. He describes the scene as filling him with a “delicious novelty of emotion,” as if the crowds rushing by are in some way transporting him or giving him a transcendent emotional experience. This response is reminiscent of a common theme of Romantic literature—the Sublime—that refers to an encounter with something greater than oneself that reminds them of their own smallness in the grand scheme of things, leading to self-transcendence. However, in Romantic literature, the Sublime is usually experienced in response to the grandeur of nature—vast mountain ranges, plunging chasms, and, indeed, the sweeping expanse of the ocean. The narrator is subverting this convention by having a Sublime response to an urban phenomenon rather than a natural one.
The ocean can, in addition to being a source of awe, be a force of terror. A person is in danger of drowning in the sea—and, similarly, one might lose themselves in the rush of a dense crowd. Oceans have uncharted depths with dangerous, unseen predators lurking beneath, and by metaphorically comparing the crowds of London with an ocean, the narrator highlights the eerie unpredictability of large groups of people. Urban crowds are made up of strangers with uncharted depths of their own: unknown histories, motives, and goals. Crowds, as places of anonymity, are also the perfect place to hide or commit an unseen crime. The narrator recognizes this and reflects at the end of the story that the old man is “the type and genius of deep crime. He refuses to be alone. He is the man of the crowd.” By refusing to be alone, the old man is able to blend into the anonymous crowds of the city and escape detection for his mysterious crime.
