Fol was born in a wealthy banking family in Geneva then living at St. Mandé, near Paris where his father Etienne-Joseph worked.

His mother died when he was six years old and he went to secondary school in Geneva where he was influenced by Edouard Claparède and François Jules Pictet de la Rive (1809–1872).

On his return to Europe he undertook medical studies in Heidelberg and completed them by obtaining his diploma in 1869 in Zurich and Berlin.

[4] Coming from a wealthy family he did not practice medicine and instead established a personal laboratory in Messina where he studied radiolarians.

In 1886, he resigned from his post in Geneva to devote himself entirely to his research in Villefranche-sur-Mer where, in 1880, he had established a small marine laboratory with Jules Henri Barrois (1852–1943).

Funded partly by the French government to carry out a study of distribution of sponges on the Tunisian and Greek coasts, Fol departed Le Havre on his new yacht, l' Aster, on March 13, 1892, accompanied by several team members.

The barometer properly measured mercury, the pressure to which the apparatus had been submitted, and the determination of the depth of compressible liquid within the device.

Mercury, along the assumed temperature of the water at the sea bottom, must remain at the stage with the hole in the pointed stopper within the large reservoir.