In former times, mostly before the end of the 19th century, many speculations were made about the height of the Earth's atmosphere. Scientists also discussed the height of the auroras, which were often observed in middle Europe. Mostly, people thought the auroras were manifestations of the lower Earth's atmosphere, and that they formed a circle inside of it. Only a few speculations were devoted to the exact height and nature of these phenomena. They were thought to be signs from God, until the appearance of the aurora on 17 March 1716 (for detail, see Schröder ).