 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.