The Real da Vinci Code

In the Da Vinci Code movie, a Harvard professor exposes a conspiracy to keep the secrets in Leonardo da Vinci's manuscripts from becoming public. There was a Real Da Vinci Code story with a real Harvard professor and a real conspiracy to bury the secrets in da Vinci's manuscripts. The bombshell in Da Vinci's manuscripts was his writings on science, not religion. The manuscripts showed that Da Vinci knew scientific concepts centuries ahead of their supposed discovery. The secrets of the manuscripts had been buried for centuries but powerful forces on both sides of the Atlantic ensured that it would be buried for several more decades. The story of how the secrets found the light of day is the Real da Vinci Code.

In the early twentieth century, Pierre Duhem discovered that da Vinci's manuscripts referenced medieval philosophers known as the Parisian Doctors. They clearly knew scientific concepts that were supposed to have been discovered centuries later by Galileo and Newton. The discovery was not welcomed. At the time, historians of science believed that the Middle Ages was a 'Dark Age'. Duhem died in 1916. Publication of his final manuscripts was stopped and referencing his historical work became taboo. Duhem's daughter, Helene, could not sit with this. What followed was decades of battle with academic elites in her native France and at Harvard. Her final gamble was to enlist Louis de Broglie, the Nobel Prize winning nuclear physicist, to help pressure the publishers. The saga ended in 1954, 38 years after her father's death.

Pierre Duhem's road to becoming a persona non grata was innocent enough. His early historical work centered on Leonardo da Vinci's scientific works. He started with the same bias as his contemporaries; that important scientific developments had not occurred in Medieval Europe [_1_] . But Duhem was meticulous. 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 that had been attributed to 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 history of science journals over the next forty years.

Duhem's fall from grace was dramatic. Only a few years earlier he had been welcomed as as a new light. With good reason. Pierre Duhem had already made important contribution in physics, economics and philosophy of science [_2_] . 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 Isis, a history of science journal. George Sarton, the editor of Isis 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. Later volumes of System du Monde 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.

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?).

In Codex Atlanticus, Leonardo referenced Albert of Saxony to help him understand the motion of the projectile fired from his mega-crossbow (see image below). Albert was one of several Parisian doctors that had written on impetus. There were many references to Parisian Doctors 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. The discussion of Duhem's ideas in historical circles needed to be shut down, too. George Sarton was the one person that could accomplish this. 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. 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. 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.