JACOB PIETER DEN HARTOG

July 23, 1901–March 17, 1989

BY STEPHEN H. CRANDALL

ALTHOUGH I HAD STUDIED his book Mechanical Vibrations in 1940 when I was an undergraduate at Stevens, I did not meet Professor Den Hartog until the fall of 1946 when I joined the faculty of the mechanical engineering department at MIT. Den Hartog had himself come to MIT only a year earlier after serving in the navy during the war. Twenty years my senior and already world famous, he was both an inspiring role model and a gracious mentor. He was internationally famous as a vibration consultant with an uncanny ability to identify and explain the cause of a mysterious vibration. But, above all, Den Hartog was a consummate teacher. He could hold the attention of a single colleague or a class of a hundred students as he explained a particular mechanism and wrapped his audience in the sheer fun of imagining how it would move and why. He taught dynamics by creating vivid images of particular cases that dramatized generic concepts. Generations of students were enriched by his verve, wit, and captivating physical insight.

Jacob P. Den Hartog was born in Ambarawa on the island of Java in the Dutch East Indies on July 23, 1901. His father, Maarten, had been a school teacher in Amsterdam until he was dismissed because of radical activity. Maarten had been



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