Read the Passage and answer the question.

Stephen and Joseph Montgolfier were papermakers, but they had been interested in flying for many years. One night, in 1782, Joseph noticed something that gave him an idea. He was sitting in front of the fire when he saw some small pieces of scorched paper being carried up the chimney.

Soon afterward, the brothers conducted an experiment. They lit a fire under a small silk bag, which was open at the bottom; at once, the bag rose to the ceiling. After this, Stephen and Joseph conducted many more experiments, both indoors and in the open air. Eventually, they built a huge balloon of linen and paper. On June 5th, 1783, they launched their balloon in the village of Annonay.

Which specific detail in the above passage describes the first experiment the brothers did?