context: Between 1878 and 1880, a French historian and member of the Académie française, Maxime Du Camp, wrote Les Convulsions de Paris. Du Camp had witnessed the last days of the Commune, went inside the Tuileries Palace shortly after the fires were put out, witnessed the executions of Communards by soldiers, and the bodies in the streets. He studied the question of the number of dead, and studied the records of the office of inspection of the Paris cemeteries, which was in charge of burying the dead. Based on their records, he reported that between 20 and 30 May, 5,339 corpses of Communards had been taken from the streets or Paris morgue to the city cemeteries for burial. Between 24 May and 6 September, the office of inspection of cemeteries reported that an additional 1,328 corpses were exhumed from temporary graves at 48 sites, including 754 corpses inside the old quarries near Parc des Buttes-Chaumont, for a total of 6,667. Modern Marxist critics attacked du Camp and his book; Collette Wilson called it "a key text in the construction and promulgation of the reactionary memory of the Commune" and Paul Lidsky called it "the bible of the anti-Communard literature." In 2012, however, historian Robert Tombs made a new study of the Paris cemetery records and placed the number killed between 6,000 and 7,000, confirming du Camps research. Jacques Rougerie, who had earlier accepted the 20,000 figure, wrote in 2014, "the number ten thousand victims seems today the most plausible; it remains an enormous number for the time."
question: Across how many years did Maxime Du Camp write Les Convulsions de Paris?
answer: 2