Benedict Carey in The New York Times:
The reign of King Louis Philippe, the last king of France, came to an abrupt and ignominious end on Feb. 24, 1848, after days of increasingly violent demonstrations in Paris and months of mounting agitation with the government’s policies. The protesters surging through the city at first were fairly orderly: students chanting, well-dressed men and women strolling, troublemakers breaking windows and looting. But late in the evening of Feb. 23, the tide turned dark. Soldiers had fired on the crowd near the Hôtel des Capucines, leaving scores of men and women gravely wounded. Some blocks away, a journalist was “startled by the aspect of a gentleman who, without his hat, ran madly into the middle of the street, and began to harangue the passers-by. ‘To arms!’ he cried. ‘We are betrayed.’”
“The effect was electric,” the journalist wrote later. “Each man shook his neighbor by the hand, and far and wide the word was given that the whole system must fall.”
Several decades later, in 1895, those events became grist for one of the first concerted scholarly efforts to understand the mob mentality, Gustave Le Bon’s “The Crowd: A Study of the Popular Mind.” Ever since, social scientists have sought to describe the dynamics of humans en masse. What, independent of police provocation, causes a seemingly peaceful group of people to turn violent? How coherent in their purpose are crowds? Why and how does a crowd become a mob?