The mood of “The Machine Stops” shifts from lighthearted to solemn over the course of the story as Vashti reckons with her relationship to her rebellious son Kuno and the Machine that controls their lives. The lighthearted, easeful mood comes across in the opening paragraph of the story as the narrator sets the scene:
There are no apertures for ventilation, yet the air is fresh. There are no musical instruments, and yet, at the moment that my meditation opens, this room is throbbing with melodious sounds. An arm-chair is in the centre, by its side a reading-desk—that is all the furniture. And in the arm-chair there sits a swaddled lump of flesh—a woman, about five feet high, with a face as white as a fungus. It is to her that the little room belongs.
Descriptions like “the air is fresh” and the “room is throbbing with melodious sounds” encourage readers to feel calm and at ease. Overall, this is a positive portrait of life in the underground society controlled by the Machine. That said, even here there are hints that things may not be as good as they seem, such as the detail that Vashti is “as white as a fungus.” This is not a very flattering comparison and also suggests (correctly) that she has not seen the sun in a very long time.
Vashti’s sense of unease increases over the course of the story as Kuno forces her to visit him halfway across the world (something she does not want to do) and reveals that he made an unsupervised trip to the earth’s surface because he is desperate to directly experience the natural world. The mood shifts into an even more anxious register as, after a time jump of several years, Vashti and Kuno notice the Machine start to show signs of failure.
By the end of the story, as the Machine fully fails and the underground society combusts, killing Vashti and Kuno in the process, the mood becomes mournful and solemn. The narrator notes how the two characters, in their final moments, “wept for humanity” and “could not bear that this should be the end” when they finally “knew what had been important on the earth," specifically human connection and a direct relationship with the natural world.