Correspondence between de Saint-Venant and Boussinesq 2: Boussinesq's professional and private life up to 1886

Abstract

Joseph Boussinesq is among the great physicists of the late 19th and the early 20th centuries, mainly due to his novel techniques to mathematically solve complicated equations by an adopted method of approximations. He has scientifically worked in all fields of physics, except for electro-dynamics. His writings are difficult to read due to overlong sentences and complicated formulations. He therefore does not count to the readers' favorite author. Boussinesq's work can, alternatively, be approached by a correspondence between two 19th century scientists, de Saint-Venant and Boussinesq. Their well-known papers are thus commented from the point of development of their theories; the input of both scientists is evidenced by their writings, and comments of both to each other. The age difference of the two was 45 years, the experienced engineer de Saint-Venant, and the mathematician Boussinesq, two eminent researchers, met to discuss not only problems in hydraulics, but in physics generally. In addition, their correspondence embraced questions in ethics, religion, history of sciences, and personal news. The life of Boussinesq is poorly documented, given his shyness and his privacy. The letters of the Correspondence reveal many details, however, that this venue was selected as the basis of this paper, ending with Saint-Venant's death in 1886. The topics discussed include Boussinesq's early career until Saint-Venant became part of his life, by asking questions on one of his first papers. They felt attached to each other, so that numerous letters were exchanged. Although others are missing in the Correspondence, the entire collection allows for an almost complete view on the life and career of Boussinesq. His years at the College of Gap and at the University of Lille are considered. The last days of Saint-Venant are commented then both in terms of the master of mechanics, and his great steps made for Boussinesq to enter the Sorbonne University in Paris. The present work is concluded with a hardly known obituary of more private than professional origin, by which the many facts are evidenced by one of his friends.