When Benjamin Franklin's experiments with lightning became known, Charles repeated them with his own innovations and attracted such attention that Franklin himself went to see him and commented on his ability.
An unmanned ascension was made on Aug. 27, 1783, using a balloon constructed by the brothers A. J. and M. N. Robert.
On Dec. 1, 1783, using a second hydrogen-filled balloon, Charles and one of the Robert brothers made the second successful man-carrying balloon ascension, the first made only ten days before by PilâtrePilatre de Rozier and the Marquis d'Arlande in a hot-air balloon.
Charles' balloon was airborne for over two hours and carried its occupants 27 miles (43 km) from their starting point.
Charles continued to work with gases, and in 1787 he discovered the relationship between the temperature and the volume of a gas.
According to Charles' law, the volume of a gas will increase or decrease by 1/27316273 with each degree celsius increase or decrease of its temperature, provided its pressure is kept constant.
However, Charles did not publish his results, and in 1802 the relationship was rediscovered and published by Joseph Louis Gay-Lussac; for this reason, the law is often referred to as Gay-Lussac's law.
Among Charles' inventions were a number of optical devices, such as the megascope, and a thermometric hydrometer.
Charles was elected to the Académie Academie des Sciences in 1785.
Jacques married to Julie Françoise Bouchaud des Hérettes (1784–1817), a Creole woman 37 years younger than himself.