In the Da Vinci Code, a Harvard professor exposes a conspiracy to cover up secrets hidden in Leonardo da Vinci's unpublished manuscripts. There was a Real Da Vinci Code story with a real Harvard professor, a real heroine, and a real conspiracy to prevent the secrets in da Vinci's manuscripts from becoming public. To this day, the story is rarely told.
In the early twentieth century, Pierre Duhem discovered many references in da Vinci's manuscripts to medieval philosophers. These philosophers had proposed concepts that had been credited to the heroes of the Scientific Revolution, Galileo and Newton. Powerful figures in academia prevented this discovery from being published or discussed. Some of the actors in this drama were very famous. Louis de Broglie was a Nobel Prize winning physicist. George Sarton, a Harvard professor, is known as the father of the History of Science. The heroine of the story wasn't famous. Pierre Duhem's daughter, Helene, decided that her father's unpublished work must be published. This meant taking on the academic elites at Harvard and the University of Paris.
Pierre Duhem was a rare genius. Before turning his attention to the history of science, Pierre Duhem had already made important contributions in physics, economics and philosophy of science [_1_] . One can hardly think of a better candidate for a historian of science; accomplished in both Math and Physics, meticulous in his research, and aware of both the cultural and philosophical issues in science.
Duhem's early historical work was well received. He wrote books on the history of mechanics and several on Leonardo da Vinci before attempting the massive 10-volume System du Monde. The first volume, dealing with Greek science, was sent to George Sarton for review. George Sarton was editor of an important journal on the history of science, Isis. Sarton gave the volume a very positive review and even let Duhem know that he was looking forward to the other volumes.
The first volume of System du Monde was the last volume that would be reviewed by Isis. Duhem would become a persona non grata. Duhem's work suggested that science may have originated centuries earlier than thought, by clerics in the 'dark ages'. Historians of science from that time were heavily invested in the Dark Age and Conflict Thesis narratives and Duhem's discoveries challenged both narratives.
Pierre Duhem's road to being shunned was innocent enough. His early historical work centered on Leonardo da Vinci's scientific works. He started his work with the common bias that important scientific developments had not occurred in Medieval Europe [_2_] . Duhem was a meticulous researcher. If Leonardo da Vinci referred to a source in his works, Duhem would track it to its original source and beyond. This lead Duhem from Da Vinci to medieval physicists that were proposing concepts associated with more modern scientists such as Galileo and Newton. This was a challenge to the common narrative of the history of science. Duhem died before the final volumes of System du Monde were published. The manuscripts for the final volumes were blocked from publication and his name and work was rarely mentioned in Isis over the next forty years.
What was in the Da Vinci Codices that was so threatening. It was the Parisian Doctors. This was a group of priests and bishops from the fourteenth century that had written extensively on classical mechanics. They had formulated Newton's First Law of Motion almost three hundred years before Newton had [_3_] . They had defined constantly accelerated motion centuries before Galileo. Galileo's description and geometric proof of the Odd Number Rule was largely the same as those of the Parisian Doctor, Bishop Oresme. We know that Galileo knew of the Parisian Doctors' work from his own writings. There was another threat posed by the Doctors. There was a direct line from the Parisian Doctors to another group, the Oxford Calculators (see The Calculatores). This was another group of priests and bishops studying classical mechanics. They had developed the mean speed theorem centuries before Galileo had proposed it (see How original is Galileo’s work on kinematics?).
The diagram of Leonardo's mega-crossbow shown below is from his Codex Atlanticus. Duhem discovered that Leonardo was referencing Albert of Saxony, a Parisian doctor, to help him understand the motion of the projectile fired from various positions. Albert had written on the subject of impetus along with other Parisian doctors. Duhem had found references to other medieval philosophers associated with the University of Paris in Leonardo's Codices.
The answer to the "Duhem Problem" was censorship. Duhem would not be published and not discussed. Duhem's publisher, Hermann et Cie, refused to publish the final volumes of his Systeme du Monde. The excuse given was financial hardship. Abel Rey, the head of the Institute d'Histoire des Sciences at the Sorbonne, knew the real reason. Hermann et Cie was being pressured by very powerful anti-clerical elements in the French government and academe not to promise publication of his work [_4_] . Medieval church clerics making important advances in the science of mechanics did not fit well with the accepted narrative. Abel Rey is one of the heroes of the story. Abel Rey was himself anti-clerical. This did not stop him from supporting Helene Duhem's 40 year long fight to publish her father's last works.
Blocking the publication of Duhem's final works was not going to be enough to quash the discussion of his ideas. He had already published many works on medieval science. There was one man that could curtail the discussion of Pierre Duhem's ideas, George Sarton. Being a professor of History of Science at Harvard University made him influential in what was taught and learned about the history of science at Harvard and other universities. His journal, Isis, had become the most important journal on the History of Science. As editor he influenced who and what were discussed in the discipline. With Duhem's death, Sarton became the leading figure in the study of medieval science. Who he did and didn't reference made a difference.
The Isis Files explores the volumes of Isis during Sarton's time as editor. The mention of Duhem was very rare, even in the references at the end of articles. Today Duhem is the most commonly referenced historian from the notable historians of medieval science in Sarton's time [_5_] . Sarton authored several large volumes of work on medieval science. In some of Sarton's works on science in the middle ages, Duhem and his work aren't mentioned at all and in others he is only very rarely referenced.
If the managers at Hermann Cie and George Sarton were successful in their censorship of Pierre Duhem, how do we know of Pierre Duhem? When Duhem died in 1916, he left behind a daughter. Helene Duhem was very dedicated to her father and very stubborn. She knew that he had left 5 unpublished manuscripts on his death that were in publishable form. The French Academy of Sciences had analyzed them. She was determined that they would be published.
Duhem died during World War I. Understandably, publishing manuscripts on medieval history is not a priority during a war. The end of war didn't seem to help matters. Hermann et Cie. always had an excuse. This went on for two decades. Helene Duhem never stopped trying to find allies to pressure Hermann to publish. The low point came with World War II, when she feared that the manuscripts would be lost. With the end of the war came more hope. Hermann et Cie. still made excuses. Helene, not knowing how to quit, enlisted the support of one of the great nuclear physicists of the twentieth century, Louis de Broglie. Even the stature of this Nobel laureate was not enough. de Broglie had to use his position as the Secretary of the French Academy of Sciences to threaten Hermann with a lawsuit. The final volumes were published in March, 1954. The real da Vinci Code story had ended; 38 years after it began.