Twenty-one of the thirty-three official pavilions were devoted to technology and the sciences. Among the most popular was the Palace of Optics, whose main attractions included the Great Paris Exposition Telescope, which enlarged the image of the moon ten thousand times. The image was projected on a screen 144 square meters in size, in a hall which seated two thousand visitors. This telescope was the largest refracting telescope at that time. The optical tube assembly was 60 meters long and 1.5 meters in diameter, and was fixed in place due to its mass. Light from the sky was sent into the tube by a movable 2-meter mirror.