This is the English translation of the book Henri Poincaré une biograhie au(x) quotidien(s), published in French by Ellipses in 2012. In this translation a part about the pun that can be made in French about "point" (point) - "carré" (square) and Poincaré's name has been left out since there is no point in translating that into English.
Henri Poincaré was not only a mathematician, but alo a physicist, an astronomer, and a philosopher. He was a member of the Académie française, a universal thinker and a public figure. No wonder that newspapers reported on his activities and journalists asked about his opinion on many things. Of course most of these quotes are from the French papers but since he got a world reputation also in the US Poincaré was `newsworthy'. So, it is quite possible to use these articles and other citations from his own work, his letters and comments and responses from his colleagues to sketch a biographic portrait of the man and his work. Most of the text consists of these quotes, and the authors have written their text in between to comment and sketch the context of the (sometimes long) block quotations.
The book has four main parts. The first one is about the early years: his family and childhood. Of course there are no newspaper quotes here, but there is his birth certificate and school reports from the École des Mines and there are reports from when he was a mine inspector in Vesoul. For example we learn that his official birth name was Henry and that his name has been misspelled on many official documents.
Part two is about Poincaré as a professor and a scientist. He became lecturer at the university of Caen but was more interested in research than in teaching. There is a discussion of his work on Fuchsian functions (named after Lazarus Fuchs) which lead to a dispute with Felix Klein who claimed the name Kleinian functions to be more appropriate since he was the first to study them but Poincaré stuck to his original naming. He submitted this work for the Grand prix de mathématiques (which he did not win). Later he moved to the Sorbonne and shifted his work to (nonlinear) differential equations and dynamical systems. When king Oscar II of Sweden issued a competition for a solution of the `three body problem', Poincaré submitted a memoir, although not completely solving the problem, he nevertheless won the prize. When the paper was later submitted to Acta Mathematica an error was detected that took him ten years to deal with. This investigation lead to the discovery and first understanding of chaotic systems. The mistake in his paper was well known among mathematicians, but was somewhat covered up for the broader public since Poincaré had won the prize and got worldwide recognition already.
Part three deals with Poincaré as a public figure. In the dispute of whether the zero meridian would be the one of Greenwich or the one of Paris, Poincaré as a member of the Bureau des Longitudes pointed out that Argentan is a French town that lies precisely on the Greenwich meridian, so that by adopting the Greenwich meridian, one could use in France the time of Argentan. Another point of discussion was the flattening of the earth. A new mission was sent out to revise an earlier measure of the meridian of Quito. Poincaré was the reporter and his speech at the Academy is reproduced in full. The dispute about the rotation of the earth was on a more philosophical level. Poincaré questioned the existence of absolute space. It can not be considered a `fact' since it can not be proved by a direct experiment. In that sense, the rotation of the earth is not a fact. Of course the metaphysical context was easily misunderstood and a lively controversy in the newspapers is reported. This dispute has haunted Poincaré for a long time. More generally, a chapter is devoted to the reviews and criticisms of Poincaré's philosophical work. This was published in three books: La science et l’hypothèse (1902), La valeur de la science (1905), and Science et méthode (1908). His recognition as a philosopher was not as smooth as it was to establish his fame as a mathematician and astronomer.
The fourth part about his social engagement starts with the Dreyfus affair. A Jewish captain of the French army was falsely accused and condemned for high treason since he allegedly had passed on secret information to a German colonel. This was juicy stuff for the newspapers and France was divided in two camps. The French intelligentsia got involved, taking up the defense of Dreyfus gathering around the flag of Emile Zola's J'Accuse, the title of an open letter in the newspaper l'Aurore addressed to the French president. Painlevé, Darboux, Appell, and Poincaré were consulted as experts in the trial. The true culprit was identified and Dreyfus reinstated after 12 years of controversy.
This boosted Poincaré's reputation even more and journalists expected him to have an opinion on many other issues even if they were only remotely related to mathematics. This part also has extensive reports on Poincaré's election as a member of the Académie frainçaise and on his views on education.
As the authors say themselves, this is anything but a complete biography. It is is a selection of some scattered fragments. It is also not always easy to distinguish really specialized journals from the journals for the "general public". They had to be aware of the different political signatures of the newspapers to give the proper background information. They also had to make a selection among all that has been published by Poincaré, about Poincaré and about all the mathematical, philosophical, social, and political issues in which Poincaré was involved. On the other hand, by mainly quoting from what was printed in the media for the general public, we get an idea of the person as he was perceived by the people of his time. These are often aspects that are not touched upon in other biographies that concentrate on facts and on the importance and the contents of his scientific work. This book is a welcome addition to the many biographies of Poincaré that exist already. By using footlight spots, instead of the spots hanging from the scientific ceiling, it sheds a light on Poincaré from a different perspective that we do not find elsewhere.