Paris in the 18th century Paris from across Europe and from the United States to share ideas; Benjamin Franklin came in 1766 to meet with Voltaire and to talk about his experiments with electricity. The 18th century in Paris was a particularly inventive period. Some of the discoveries of Paris scientists, particularly in the field of chemistry, were quickly put to practical use; the experiments of Lavoisier were used to create the first modern chemical plants in Paris, and the production of hydrogen gas enabled the Montgolfier Brothers to launch the first manned flight in a hot-air balloon on 21 November 1783, from the Château
Hot air balloon basket-less balloons (called "Hoppers" or "Cloudhoppers") have as little as of envelope volume; for a perfect sphere the radius would be around . At the other end of the scale, balloons used by commercial sightseeing operations may be able to carry well over two dozen people, with envelope volumes of up to . The most-used size is about , and can carry 3 to 5 people. The top of the balloon usually has a vent of some sort, enabling the pilot to release hot air to slow an ascent, start a descent, or increase the rate of descent, usually for