![]() Finally, when Thomson reduced the minuscule air pressure inside the tube even further, spots produced by the canal rays suddenly separated and resolved themselves into a series of parabolic smears. Ultimately, placing a photographic plate inside the vacuum tube itself proved most effective. ![]() Then he developed various techniques to record the faint impression the rays made when they hit the wall of the tube after being deflected by powerful magnetic and electric fields. First, he collimated the rays, lining them up by extending the hole in the cathode into a long, narrow tube. Little was known about the nature of these particles until Thomson began a series of improvements to the apparatus. But researchers soon found that a stronger magnetic field deflected the rays, implying that they were charged particles like electrons but immensely more massive. At first the rays were enigmatic, since unlike electrons they were not affected by a magnetic field. As the flow of electrons left the cathode, unknown particles flowed in the opposite direction, passing through the holes. They were produced by drilling channels ( Kanäle, or canals) in the cathode of a cathode-ray tube (a sealed glass tube with almost all its air removed and with a cathode and anode added). ![]() Originally called Kanalstrahlen, Thomson’s rays had first been described by Eugen Goldstein in 1886. Thomson’s starting point-the “rays of positive electricity’’ from his title-was in a sense the opposite of the electrons (then known as cathode rays) he had won fame for discovering. After receiving the Nobel Prize in physics days before his 50th birthday in 1906, Thomson embarked on a new line of research, arguably invented mass spectrometry, and published the field’s foundational text, Rays of Positive Electricity and Their Application to Chemical Analyses, exactly 100 years ago this year. Thomson represents a glaring contradiction to this sentiment. Albert Einstein once remarked that “a person who has not made his great contribution to science before the age of thirty will never do so.” J.
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