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JACOB PIETER DEN HARTOG
1 901-1 989
BY ROBERT CANNON AND STEPHEN CRANDALL
ACOB PlETER DEN ~TOG, internationally famous vibration
consultant, author, and teacher, died March 17, 1989, after a
long illness. He authored the best-known textbook on mechan-
ical vibrations and was widely acclaimed for his skill in perceiving
the mechanisms underlying unexpected vibration problems in
machines and structures.
Yet above all, Professor Den Hartog was a consummate teach-
er. He would get you raptly engrossed in some inscrutable
mechanical system, and envelop you in the sheer fun of imagin-
ing the ways in which itwill move, end why physically. It's called
dynamics; and he taught each of its secretswith words that always
created a vivid image of yet another particular mechanism whose
intriguing behavior dramatized a generic concept. And you
never forgot that image; and that's why that concept was now
yours in whatever new guise you encountered it. Generations of
students were enriched by this man of verve, of wit, of captivating
physical insight, who was affectionately known as Jaappy (pro-
nounced Yahppy, the Dutch diminutive of Jacob).
Den Hartog was born on July 23, 1901, in the Netherlands East
Indies (now Indonesia), where he lived until the family returned
to Holland in 1916. He did his undergraduate study at Delft
Polytechnical Institute in Holland, graduating with a degree in
electrical engineering in 1924. Because of poor economic condi-
tions in Holland at that time, he emigrated immediately to the
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MEMORIAL TRIBUTES
United States. Through a series of fortunate accidents, he soon
fount! himself in Pittsburgh working for Westinghouse as the
assistant to a Russian emigre, Stephen P. Timoshenko, twenty
years his senior and venerated world guru in applied mechanics.
Timoshenko's selection process was to compose a written exam-
ination for the group of Westinghouse candidates to try their
hand at. When he saw Den Hartog's solution set he pronounced,
"Bring me this man!"
Timoshenko assigned the young Dutchman to a gamut of
vibration problems in electric motors and generators, hydraulic
power machinery, railroad electrification, steam turbines, and
the like. And his repertoire of physical images began to take
shape. The sequence, Dr. Den Hartog explained, was that "one
clay in freshman physics at Delft the professor slowly charged up
two great spheres, one at each end of the lecture table, until
suddenly a great bolt of electricity leaped between them. At that
instant ~ became an electrical engineer; and it took Stephen
Timoshenko three years in Pittsburgh to convert me back to
mechanical." Later a son was named Stephen Den Hartog.
While at Westinghouse, Jacob Pieter studied mathematics at
the University of Pittsburgh in the evenings, completing his
Ph.D. in 1929 with a thesis on nonlinear vibrations.
In 1931 he spent a sabbatical year in Gottingen in the labora-
tory of Professor Prandtl. On his return in 1932 he joined the
faculty of Harvard University and began his teaching career,
lecturing on vibrations and assembling an extensive collection
of vibration demonstration models. His lectures had such a
reputation that professors from the nearby Massachusetts Insti-
tute of Technology (MIT) would take the trolley across town to
sit in with the Harvard students. Here he publisher! the first
edition of his famous text Mechanical Vibrations in 1934. He had
also published another (lozen papers before the signs of impend-
ing war persuaded him that he could be more useful (and have
more fun) by serving in the military than by remaining a civilian.
He accepted a reserve commission in the U.S. Navy in 1939.
From 1941 to 1944 he was on active full-time duty on ship
vibration problems in the Bureau of Ships, working in the
nation's navy yards and ships as well as in naval machinery
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JACOB PIETER DEN HARTOG
83
manufacturing plants all over the country. In 1945 he served in
Europe on the Naval Technical Mission, Europe.
When the war was over, Captain Den Hartog returned with
great energy and enthusiasm to a civilian life of consulting, and
to a new and rest-of-his-life—post as professor of mechanical
engineering at MIT. He served also as department head from
1954 to 195S, but his first love was lecturing and tackling
challenging consulting problems.
His consulting life was one of helping solve mysterious dynam-
ic problems. Usually something was inexplicably vibrating in a
systemjust built a submarine's drive shaft, or an electric power
transmission line, or a very tall chimney. The proprietor would
put the project on "hoIcI" and call Professor Den Hartog. He
would come on the next overnight train and watch the phenom-
enon intently and ask questions. In his remarkable mind an
image would develop of the simple essence of the phenomenon,
of cause and effect. He would of course share his surgical insight
in real time, in simple terms, and with a unique and endearing
wit.
And then he would! share it with his students; it would become
part of the delightful set of case studies with which he wove the
fabric offundamental concepts. And finally, of course, they took
their place in the body of his written contributions. There came
a series of landmark papers in nonlinear vibrations of electrical
machinery, of turbine blades, of tall stacks with von Karman
vortices, of piping systems, of the foundations for elevated
structures, of great furnace walls and tubes, and on torsional
vibration ciampers and dynamic vibration absorbers. There
came three new textbooks. And there came successively three
new American editions of the venerable Mechanical Vibrations,
which had also fifteen foreign editions in eleven languages. The
style is so simple and direct as the reader is lecI skillfully (and
impishly) to the essential heart of each problem.
Thus Den Hartog's precious legacy came in three parts: his
wealth of new physical insights into mechanical vibrations, the
highly readable way he committed them to prose, and the solid,
endearing (and entertainingly wayinwhich he shared themwith
the generations of lucky students who got to study with him.
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MEMORIAL TRIBUTES
In the 1940s Professor Den Hartog's fame as lecturer spread
rapidly; he was invited to lecture in most leading American
universities and in approximately sixty foreign universities.
He spent four months in 1955 as a Fulbright visiting lecturer
in Japan and was invited to give the Thomas Hawksley Lecture in
London in 1957, the first American to be so honored.
Happy loved music, was a good amateur violinist, and a
marvelous raconteur. He and his wife, Beppie, and sons, Maarten
and Stephen, also loved to act as unofficial ambassadors to
foreign students and scientists. They owned an islancl in the
middle of Lake Winnipesaukee, which they used to entertain
visitors. For many foreign scientists their most vivid memory of
the United States is of teeing bundled into a car, driven up to New
Hampshire, seated in a canoe, and paddler! across the lake to
spend an iclyIlic weekend on the island.
Jacob Den Hartog's talents were widely recognized, and he
received many honors from his fellow engineers, from universi-
ties, and from prestigious academies. From the American Soci-
ety of Mechanical Engineers (ASME), in addition to the Timo-
shenko Medal in 1972, he received the Charles Russ Richards
Memorial Award, the Worcester Reed Warner Medal, and the
American Society of Mechanical Engineers Medal. The Arneri-
can Society for Engineering Education awarclect him the Lamme
Award, and the Acoustical Society of America awarded him the
Trent-Crede Award. He was an honorary member of ASME and
the Japan Society of Mechanical Engineers, and a fellow of the
British Institution of Mechanical Engineers. He was awarded
honorary doctorates from Carnegie Institute of Technology, the
University of Ghent, the Technical University of Delft, Salford
University, and the University of NewcastIe-Upon-Tyne. He was
elected to both the U.S. National Academy of Sciences and the
U.S. National Academy of Engineering, to the American Acad-
emy of Arts and Sciences, and to the Royal Dutch Academy of
Arts and Sciences. At the end of his career, he received three
major awards during his eightieth year: the James Watt Tnterna-
tional Medal from the British Institution of Mechanical Engi-
neers, the Founclers Award from the U.S. National Academy of
Engineering, and the Order of the Rising Sun from the Emperor
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JACOB PIETER DEN HARTOG
85
of Japan. He is remembered also by MIT's I. P. Den Hartog
Distinguished Educator award to recognize "excellence . . . in the
tradition of Den Hartog," and the ASME Design Engineering
Division's Jacob P. Den Hartog Award for "sustained meritorious
contributions to vibration engineering," of which he was first
recipient.
Some of us remember best that he told us, "Spend your life
teaching, and you'll have a lot of fun." For we dicI. And he was
right.
Representative terms from entire chapter:
mechanical engineers
