Émile Hilaire Amagat (2 January 1841 – 15 February 1915) was a Frenchphysicist. 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.