Symbolism, Imagery, Allegory
Whenever the Professor seems to be really confident in how awesome he is, he has a way of going out onto the street and finding it "peopled by a mere fraction of an immense multitude" (5.2). The Professor is super-rattled by seeing so many people walking around him, because he's scared that these people might be "impervious to sentiment, to logic, to terror, too, perhaps" (5.2).
In other words, how's he supposed to feel awesome when he's constantly reminded that no one cares about his stupid bomb? Shucks. Life is hard when you're the Professor.
Whenever the Professor sees the multitude of people in the street, he tries to reassure himself by thinking of "the refuge of his room, with its padlocked cupboard […] the hermitage of the perfect anarchist" (5.3). In other words, he can only fantasizes about how great he is when he's alone, because the sheer numbers of the London multitude are constantly reminding him that he doesn't stand out in a crowd. Womp womp.