Who was the French professor that the Robert brothers built the world's first hydrogen balloon for?
Robert brothers Les Frères Robert were two French brothers. Anne-Jean Robert (1758–1820) and Nicolas-Louis Robert (1760–1820) were the engineers who built the world's first hydrogen balloon for professor Jacques Charles; which flew from central Paris on August 27, 1783. They went on to build the world's first manned hydrogen balloon, and on 1 December 1783 Nicolas-Louis accompanied Jacques Charles on a 2-hour, 5-minute flight. Their barometer and thermometer made it the first balloon flight to provide meteorological measurements of the atmosphere above the Earth's surface.
Jean-Pierre Christin Jean-Pierre Christin (May 31, 1683 – January 19, 1755) was a French physicist, mathematician, astronomer and musician. His proposal to reverse the Celsius thermometer scale (from water boiling at 0 degrees and ice melting at 100 degrees, to water boiling at 100 degrees and ice melting at 0 degrees) was widely accepted and is still in use today.