Émile Hilaire Amagat (2 January 1841 – 15 February 1915) was a
French physicist. His doctoral thesis, published in 1872, expanded on the work of
Thomas Andrews, and included plots of the
isotherms of
carbon dioxide at high pressures. Amagat published a paper in 1877 that contradicted the current understanding at the time, concluding that the coefficient of
compressibility of fluids decreased with increasing pressure. He continued to publish data on isotherms for a number of different gases between 1879 and 1882, and invented the
hydraulic manometer, which was able to withstand up to 3200
atmospheres, as opposed to 400 atmospheres using a glass apparatus. In 1880 he published his
Law of Partial Volumes.