Whither dislocations?
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INTRODUCTION
C U R I O U S thought processes exist in the heads of those who organize anniversary symposia. A magic number like, say, 50 sets off bells in their heads. Voices talk to them. The voices tell them, "It is 50 years since dislocations were conceived. Such an immaculate conception deserves a symposium." The voices drive them on until the symposium is an actual fact. But then other voices of a darker kind are heard by them. "Your symposium has finally laid to rest its subject. Like that famous parrot, the Norwegian Blue, it is deceased, finished, of no more use." Since the organizers may have just put in a proposal on dislocations to a Granting Agency in Washington, that is a grim thought i n d e e d - especially if agency representatives were invited to the symposium. But then an up-beat voice is heard by them. "Get a guru from that mysterious, unfathomable land of the Midwest to tell us 'Whither Dislocations?' " I should tell you that information imparted by gurus may not be entirely to your taste. I am reminded of a story I recently read in a geological news journal. ~I may not have the story quite right but it concerned the encounter of an elderly guru from the East and a newly minted Ph.D. from the West who knew all the latest theories, where indeed science is headed, and who probably was traumatized by his last oral examination. They discussed a subject which has been of great interest in the past to Professor Orowan, one of the discoverers 50 years ago of dislocations. This subject is the earth beneath us, what is down there, and what is going on down there. Earthquakes, as you all believe, are caused by exuberent dislocations that move quickly from one place to another in the earth. The New Doctor drew out of the Old Guru the information his recent schooling had not taught him. The crust of the earth actually is the shell of a huge turtle who rests on a big elephant's back. When a flea enters one of the elephant's ear canals the animal flaps its ears, shakes the turtle, and thus makes an earthquake. The Ph.D. asked, perhaps not quite as respectfully as he should to a wise man, "Amazing, but there is a slight problem I hesitate to bring up with your theory. On what does the elephant stand?" The obvious answer came back, "On the back of another elephant." The next probing question, asked with somewhat less respect, "And that elephant stands on what?" To which the guru said, "I may as well complete your education right now. It's elephants all the way down."
J. WEERTMAN is Walter P. Murphy Professor of Materials Science and Engineering, Department of Materials Science and Engineering, and Professor of Geophysics, Department of Geological Sciences, Northwestern University, Evanston, IL 60201. This paper is based on a presentation made at the symposium "50th Anniversary of the Introduction of Dislocations" held at the fall meeting of the TMS-AIME in Detroit, Michigan in October 1984 under the TMSAIME Mechanical Metallurgy and Physical Metallurgy Committees. METALLURGICALTRANSACTIONS A
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