(1777–1859) French physicist
Born in Paris, France, Cagniard de la Tour was educated at the Ecole Polytechnique and then spent his time as an amateur inventor. In 1819 he invented the disk siren, in which the sound is produced by air blowing through holes in a rotating disk, the pitch being determined by the speed of rotation. He made his most famous discovery in 1822; when he heated certain liquids in sealed tubes he observed that at a particular temperature and pressure the meniscus dividing liquid from vapor disappeared. Under these conditions – known as the critical state – the densities of liquid and vapor become the same and the two are identical.
In the field of biology Cagniard de la Tour discovered, independently of Theodor Schwann, the role of yeast in alcoholic fermentation. He also studied the physics of the human larynx and the sounds produced by it and invented a machine for studying bird flight.
Subjects: Science and Mathematics.