In other words, if suchĮntities don't exist then we have no plausible causal story to Tracks are there" (Cartwright, 1983, p.99). There are no electrons in the cloud chamber, I do not know why the Her discussion of the operation of a cloud chamber she states, ".if CartwrightĪlso stresses causal reasoning as part of her belief in entities. Of an entity as a criterion for belief in its existence. Hacking, as noted above, and Cartwright emphasize the manipulability Realism" proposed by Cartwright (1983) and by Hacking (1983). Postulated by the theory exist" (Sellars 1962, p. View that "to have good reason for holding a theory is ipsoįacto to have good reason for holding that the entities Reason to believe in phlogiston and caloric, substances we now have Reasons for belief in the existence of an entity or in the truth of a It is conjectural because, despite having good The position I adopt is one that might reasonably be called In the existence of electrons well before Peggy II, and I will argue Physicists were manipulating theĮlectron in Hacking's sense in the early twentieth Manipulability can often provide us with grounds for belief in a Peggy II provided polarized electrons for anĮxperiment that scattered electrons off deuterium to investigate the Polarized electrons built at the Stanford Linear Accelerator Center in Properties of the electron, was that of Peggy II, a source of Which he believed more convincing because it involved several Insufficient grounds for belief in electrons. Niobium sphere, which involves only the charge of the electron, was The changing of the charge on an oil drop or on a superconducting Hacking worried that the simple manipulation of the first quotation, Interfere in other more hypothetical parts of nature" (p. That use various well-understood causal properties of electrons to "We areĬompletely convinced of the reality of electrons when we set out toīuild - and often enough succeed in building - new kinds of device In discussing the existence of electrons Ian Hacking has written, "Soįar as I'm concerned, if you can spray them then they are real" Thomson and the Electron: A Supplement to Experiment in Physics (Stanford Encyclopedia of Philosophy/Fall 2005 Edition)Īppendix 7: Evidence for a New Entity: J.J. Another of his discoveries was the photoelectric effect.Appendix 7: Evidence for a New Entity: J.J. He found that nonconductors allow most of the waves to pass through. Hertz also noted that electrical conductors reflect the waves and that they can be focused by concave reflectors. This occurred when Hertz turned on the oscillator, producing the first transmission and reception of electromagnetic waves. The receiver was placed several yards from the oscillator.Īccording to theory, if electromagnetic waves were spreading from the oscillator sparks, they would induce a current in the loop that would send sparks across the gap. At the ends of the loop were small knobs separated by a tiny gap. To confirm this, Hertz made a simple receiver of looped wire. Hertz reasoned that, if Maxwell’s predictions were correct, electromagnetic waves would be transmitted during each series of sparks. He used an oscillator made of polished brass knobs, each connected to an induction coil and separated by a tiny gap over which sparks could leap. In 1887 Hertz designed a brilliant set of experiments tested Maxwell’s hypothesis. In 1883 Hertz became a lecturer in theoretical physics at the University of Kiel and two years later he was appointed professor of physics at Karlsruhe Polytechnic. James Clerk Maxwell’s mathematical theory of 1873 had predicted that electromagnetic disturbances should propagate through space at the speed of light and should exhibit the wave-like characteristics of light propagation. In the 1880s many were seeking experimental evidence to establish the equivalence of light and electromagnetic propagation. See the excellent reference Heinrich Rudolf Hertz. Heinrich Hertz’s Wireless Experiment (1887) Taken from the following HARVARD EDU LINKS
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