This seems a non-sequitur, part of a general list of items adding to Nostromo's annoyance, but it too applies to Giselle. Note that Nostromo is exasperated at Giselle's "tranquillity"; against her tranquil world he sets the existence of ensorcelling wealth and "evil" (or at least enmity). I.e., for a moment he is challenging the possibility of utopia with the fact of the flawed world. Note that what calms him is a smile that shines "straight upon his heart," i.e., without passing through the physical world. The brief moment illustrates the dilemma at the core of this section of the novel: if the heart can be so good, why does the world have to be so bad?