![]() However, cathode rays moved at much slower speeds. At the time, light was “known” to be a wave that traversed the ether, and all waves and other disturbances in the ether were assumed to travel at the same speed as light. On the European continent, primarily in Germany, the light-like behavior led physicists to the conclusion that the rays were disturbances in the ether.Įach side had some experimental evidence to support its view. Crookes proposed that they were negatively charged molecules. Most British physicists concluded that the experiments indicated that the “rays” were some type of particle. Two different views of cathode rays developed. For example, they could be deflected by a magnetic field.īy D-Kuru, used under the terms of Creative Commons BY-SA 2.0 license However, the cathode rays in some ways acted differently from light. He saw that a shadow of the cross was cast on the end of the tube. Crookes inserted a Maltese cross in a tube. Just like light, the cathode rays could cast a shadow. (If you wish to see several photographs of Geissler and Crookes tubes, you should visit the Cathode Ray Tube Site.) The negative end of an electrical device was called the cathode, so these “things” became known as cathode rays and the vessels were called cathode-ray tubes. Whatever was moving seemed to behave somewhat like rays of light. One of his conclusions was that something was being emitted from the negative electrode and was moving in a straight line to the positive end of the tube. Crookes improved on the tube and conducted many experiments. One of the researchers was William Crookes (1832-1919). Sir William Crookes as drawn by Sir Leslie Ward in 1902 (public domain) The tubes used in neon lights are modern variations on Geissler tubes. These instruments might remind you of neon lights and they should. The picture below shows a drawing, published in 1869, of several different Geissler tubes. He found that the gas inside the tube would glow, with the color depending on what gas was trapped inside. Geissler connected a high voltage across the two electrodes and used another of his inventions, the vacuum pump, to decrease the pressure inside the tube. These tubes were long, sealed glass cylinders and had metal electrodes at each end. Geissler was an instrument maker who, in 1857, created electric discharge tubes. I have chosen to start the story with Heinrich Geissler (1814-1879). Because research such as this is always built on previous work, I have a difficult time knowing how far back to go. However, this discovery had its roots in research and development that date to the first half of the 19th century. The generally accepted year for the “discovery” of the electron is 1897. In this post, I will discuss the electron, how it was discovered, and some of the recent views about whether this research was really a discovery. ![]() Another - the identification of the electron as a component of matter – was the result of careful research and the development of improved technologies. We will look at each of them in future posts. Two of these discoveries – radioactivity and x-rays – were somewhat accidental. ![]() In the last decade of the 19th century, discoveries began new directions in our thinking about the composition of matter. Although one gifted scientist got the credit, he had help. In this installment on the history of atom theory, physics professor (and my dad) Dean Zollman discusses the discovery of the electron.
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