Three short lines, and a whole journey seems to vanish in them. The poem starts on the ground, with rails that "break up," as if the path forward has fallen apart. Then the engine, something heavy and made of iron, "has flown away." That's a strange and surprising image. A train is supposed to stay on its tracks, yet here it escapes upward into "gray clouds."
The speaker never says how they feel, which is part of the effect. We're left to sense it in the details. The broken rails suggest loss or interruption, while the flying engine could mean freedom, or it could mean something leaving that can't be called back. The gray clouds tint everything with quiet sadness and uncertainty. The mood is hushed and a little dreamlike, like watching something you depended on slip out of reach and not quite knowing whether to mourn it or marvel at it.