He is best known for a remark in his 1934 book Le Volume(s) des Insectes ("Insect Flight") that insect flight was impossible. He qualified as a doctor of medicine and of science, and received the diploma of superior studies in zoology. He became a professor of animal mechanics applied to aviation at the Collège de France (from 1929 to 1938), and the director of the experimental morphology laboratory and the aviation laboratory at the École pratique des hautes études in Paris.
He was responsible to the ministries of Education, Agriculture and the Interior.
The following passage appears in the introduction to Le Volume(s) des Insectes:
This translates to:
First prompted by what is done in aviation, I applied the laws of air resistance to insects, and I arrived, with Mr. Sainte-Laguë, at this conclusion that their flight is impossible.
Magnan refers to his assistant, the mathematician and engineer André Sainte-Laguë as the source of the calculations mentioned.