The effect is to make the entire narration tangible and real for the reader.
Explanation:
The intense use of descriptive details by Poe, allows the narration to be extremely detailed. This gives the reader a panaromic view of all the elements that are being narrated, so that the reader can see and feel everything that is being narrated in an efficient and detailed way. This makes the narration palpable and real, allows the reader to have an immersive and deep experience in the story.
Mallard's life would not have ended an hour later but would simply have gone on as it had been. Yet another irony at the end of the story is the diagnosis of the doctors. They say she died of "heart disease--of joy that kills
