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Galileo and the Leaning Tower of Pisa ✸ 147 8 omson, Plum-Pudding, and Electrons e learn in school that electricity is a current of subatomic particles that are negatively charged: electrons. But who discovered that and how? Just as the question of whether Pythagoras discovered anything is complex, so is the issue of what constitutes authorship of a scientific discovery. In the case of electrons, fortunately, we have plenty of documentary evidence. That evidence involves a story about the British physicist J. J. Thomson. Incidentally, I once had a problem with Thomson, when I was growing up in Puerto Rico.When I was about sixteen years old,I participated in a television quiz show with my school, and it came down to one last question, directed at me:“Which great physicist, from the beginning of the twentieth century, made breakthroughs that led other physicists to formulate theories and discoveries that later led to nuclear fission?” I puzzled over this question as the seconds ticked by, and I asked that it be repeated. Time ran out; I hesitated, and replied:“J. J. Thomson.” Wrong. The moderator expected the answer: Albert Einstein. I immediately argued that I thought that the question was ambiguous, but a producer in the shadows stopped me flat,yelling:“This is television!” Then they asked a student from the rival school:“Who was the first scientist to discover nuclear fission?” He replied:“Enrico Fermi.”And they won. Afterward, my teachers sympathized as I argued that Einstein was one of the physicists who “formulated theories that later led to nuclear fission,” and that he lived and worked until 1955, and hence that he was not“from the beginning of the twentieth century.” So I had thought that the answer should be someone who contributed to the discovery that the atom had structure, parts, and could therefore be split. (In hindsight, W 147 my guess was not good, partly because the question asked about splitting the nucleus, and J. J. Thomson did not seem to have contributed to that.) I also complained that the other student was wrong, because actually, Otto Hahn and Fritz Strassmann had split the atomic nucleus (as explicated by Lise Meitner, as I later learned). But to no avail, we still lost the game. That game-show incident now seems typical of a common disdain to check facts about the history of science. What difference does it make? This attitude shows up plainly in science classrooms. Consider the case of J. J. Thomson. In countless schoolbooks, J. J. Thomson is known for two things. He discovered the electron, and he formulated the “plum-pudding” model of the atom. One achievement was a breakaway success, the other a flop. In the early 1900s, apparently, the atom seemed to be like a faint glob of positive charge with small negative electrons stuck at random places—like raisins in that bready old English treat (plum-pudding has no plums). But schoolbooks tell us that Ernest Rutherford and his assistants falsified Thomson’s plum-pudding atom by spraying alpha particles (positively charged helium atoms) against thin gold foil. Sort of like shooting bullets at a fluffy slice of pastry. Surprisingly, some of the bullets bounced back, suggesting that the atom was really not a soft glob of fuzz but that it had a dense, hard nucleus. It’s a classic story of progress in physics. For years, Rubén Martínez (no relation to me) researched the history of the plum-pudding model of the atom. He analyzed hundreds of books and documents.Yet he found no evidence at all that J. J. Thomson ever advanced a plum-pudding model of anything.1 None of Thomson’s models of the atom resemble the pictures or accounts of the plum-pudding model that famously shows up in science books. Instead, Thomson theorized, for example, that the atom consists of a series of stacked planes on which negatively charged particles rotate in circles, around the axis of an immaterial positive sphere. The earliest appearance in print of the plum-pudding tale, found by Rubén Martínez, was in a physics textbook of 1943. If anyone did formulate an atomic model that roughly looked like plum-pudding, it was actually an older Thomson. In 1899, William Thomson (no relation to J. J.), 148 ✸ omson, Plum-Pudding, and Electrons better known as Lord Kelvin, described the atom in a way that closely resembles the plum-pudding cartoon that decades later showed up in...


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