This beam was deflected toward the positive charge and away from the negative charge, and was produced in the same way with identical properties when different metals were used for the electrodes. When high voltage was applied across the electrodes, a visible beam called a cathode ray appeared between them. This apparatus consisted of a sealed glass tube from which almost all the air had been removed the tube contained two metal electrodes. If matter were composed of atoms, what were atoms composed of? Were they the smallest particles, or was there something smaller? In the late 1800s, a number of scientists interested in questions like these investigated the electrical discharges that could be produced in low-pressure gases, with the most significant discovery made by English physicist J. Atomic Theory after the Nineteenth Century While the historical persons and dates behind these experiments can be quite interesting, it is most important to understand the concepts resulting from their work. Here, we will discuss some of those key developments, with an emphasis on application of the scientific method, as well as understanding how the experimental evidence was analyzed. Much of this came from the results of several seminal experiments that revealed the details of the internal structure of atoms. In the two centuries since Dalton developed his ideas, scientists have made significant progress in furthering our understanding of atomic theory. Define isotopes and give examples for several elements.Describe the three subatomic particles that compose atoms.Summarize and interpret the results of the experiments of Thomson, Millikan, and Rutherford.Outline milestones in the development of modern atomic theory.Thomson an experimental genius?’ ( 1986) Google Scholar, submitted to Social Studies in Science.By the end of this section, you will be able to: CrossRef Google Scholar In my thesis and a forthcoming paper, I discuss other ways in which the mechanical philosophy influenced Thomson's approach to experiment: Falconer, I., ‘J. As Wheaton has pointed out, the mechanical philosophy was implicit in Thomson and Schuster's cathode ray experiments: they assumed that macroscopic mechanical laws carried over into the microscopic realm: Wheaton, B., The Tiger and the Shark, Cambridge, 1983, p. He does not consider any experimental stimulus for the theory changes he describes, nor the influence of these theoretical commitments on Thomson's experimental work. However, Topper deals exclusively with Thomson's theoretical work. Google Scholar The last of these is particularly important for containing details of Thomson's vortex analogies and the way he transposed them from one situation to another. Thomson and the mechanical picture of nature’, Annals of Science, ( 1980), 37, p. 393 Google Scholar ‘To reason by means of images: J. #Results of cathode ray experiment archive#71–19065 ‘Commitment to mechanism: J.J.Thomson, the early years’, Archive for the History of Exact Sciences, ( 1971), 7, p. Thomson and Maxwell's Electromagnetic Theory’, Ph.D dissertation, Case Western Reserve University, 1970 Google Scholar, University Microfilms order No. CrossRef Google Scholar Topper has studied Thomson's commitment to mechanism in general, and to Maxwell in particular, in his thesis and two papers: Topper, D., ‘J. J., ‘ Mechanical explanation at the end of the nineteenth century’, Centaurus, ( 1972), 17, p. (20).ĥ5 Klein examines the status of the mechanical philosophy and visualisable analogies, particularly Maxwell's use of them: Klein, M. 510 Google Scholar ‘The disruptive discharge of electricity through gases’, Philosophical Magazine, ( 1890), V, 29, p. 371 Google Scholar ‘The passage of electricity through gases’, British Association Report, ( 1889), p. 317, 495 CrossRef Google Scholar ‘Experiments on the discharge of electricity through gases’, Proceedings of the Royal Society, ( 1887), 42, p. Schuster, A., ‘ Experiments on the discharge of electricity through gases: a sketch of a theory’ (Royal Society Bakerian Lecture), Proceedings of the Royal Society, ( 1884), 37, pp. At the relatively high pressures of Thomson's experiments, cathode rays were not a significant phenomenon, but they probably were in Schuster's experiments. Neither quotes figures for the pressures they were working at, but Schuster appears to have expended more time in evacuating his apparatus. 34 This difference between Schuster and Thomson was probably largely due to the conditions under which they performed their experiments.
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