“Only the gloom to the west, brooding over the upper reaches, became more somber every minute, as if angered by the approach of sun.” (pg. 4)
In this sentence, Conrad uses personification to create a more vivid image of the sunset around the boat. Personification is when an author takes something decidedly not-human (the weather, an object, etc.) and gives it human characteristics, such as emotion or appearance. Obviously, the “gloom” cannot actually be angry since it’s simply a part of the weather, but the reader can imagine the clouds far away over the horizon darkening like the expression of a person might darken when they became upset.