Edgar Allan Poe uses three elements, which make the mystifying atmosphere in the "Oblong Box". He uses nature, mystery, and a deep romantic love.
First, one element is nature. Nature builds itself up throughout the story. At the beginning, they had to put off the trip for a week because of the weather. On the day before the ship was originally scheduled to set sail Mr. Wyatt's wife died. Poe points that the first three or four days had fine weather. This was the calm before the storm. As the weather grew worse, Wyatt's conduct became gloomier. Poe even says he was morose. After seven days the weather worsened. The passengers expected this because the weather had been building up. Then it became a hurricane. The story is reaching a climatic point. Also, Poe states that the moon heightened the spirits of the passengers in the crisis.
Then, when Mr. Wyatt jumped overboard to get the box, the boat is swept away by the sea, and the passengers are unable to stop him. Mr. Wyatt died at the mercy of the sea.
The second element is mystery. First, he mentions there is an unusual number of ladies at sea. Adding to the mystery is the narrator's curiosity. He is amazed that Mr. Wyatt should need three rooms instead of two. He entertains two theories, one that a servant is coming along and two, that maybe there is extra baggage to valuable to be let out of his own care. Ironically, both theories are correct. There is also a mystery behind Mr. Wyatt's wife. He is astonished to find that she is plain-looking, and not at all the beautiful, intelligent woman the artist had enthusiastically described. He once again is mystified when he sees the strange shape of...