How Not to Be Wrong: The Power of Mathematical Thinking

by Jordan Ellenberg

Bertillon was appalled by the unsystematic and haphazard way in which French police identified criminal suspects. How much better and more modern it would be, Bertillon reasoned, to attach to each miscreant Frenchman a series of numerical measurements: the length and breadth of the head, the length of fingers and feet, and so on. In Bertillon’s system, each arrested suspect was measured and his data filed on cards and stored away for future use. Now, if the same man were nabbed again, identifying him was a simple matter of getting out the calipers, taking his numbers, and comparing them with the cards on file. “Aha, Mr. 15-6-56-42, thought you’d get away, didn’t you?” You can replace your name by an alias, but there’s no alias for the shape of your head. Bertillon’s system, so in keeping with the analytic spirit of the time, was adopted by the Paris Prefecture of Police in 1883, and quickly spread throughout the world. At its height, bertillonage held sway in police departments from Bucharest to Buenos Aires. “The Bertillon cabinet,” Raymond Fosdick wrote in 1915, “became the distinguishing mark of the modern police organization.” In its time, the practice was so common and uncontroversial in the United States that Justice Anthony Kennedy brought it up in his majority opinion in the 2013 case Maryland v. King,