Image from page 504 of "Practical physics" (1922)

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Identifier: practicalphysics00mill
Title: Practical physics
Year: 1922 (1920s)
Authors: Millikan, Robert Andrews Gale, Henry Gordon
Subjects: Physics
Publisher: Boston : Ginn and Co.
Contributing Library: University of British Columbia Library
Digitizing Sponsor: University of British Columbia Library

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Text Appearing Before Image:
pected if theyconsist of negatively charged particles, and when Perrin in CATHODE AND RONTGEN RAYS 439 Paris bad proved that they actually impart negative chargesto bodies on which they fall, all opposition to the projected-particle theory was abandoned. The mass and speed of theseparticles are computed from their deflectibility in magneticand electric fields. Cathode rays are then to-day universally recognized as streamsof electrons shot off from the surface of the cathode with S2Jeedswhich may reach the stupendous value of 100,000 miles per second. 499. X rays. It was in 1895 that Rontgen (see oppositep. 446) first discovered that wherever the cathode rays im-pinge upon tlie walls of a tube, or upon any obstacles placedinside the tube, they give rise to another type of mvisibleradiation which is now ,^^K\il, known under the name s^-^i;;™*^^-■-.♦ of JC rays or Bontyenrays. In the ordinaryX-ray tube (Fig. 475)a thick piece of plati-num P is placed in thecenter to serve as a tar-

Text Appearing After Image:
FiG. 475. An X-ray bulb get for the cathode rays, which, being emitted at right anglesto the concave surface of the cathode C, come to a focus ata point on the surface of this plate. This is the point at whichthe X rays are generated and from which they radiate in alldirections. The target P is sometimes made of a heavy pieceof tungsten. In order to convince ones self of the truth of this statement it is onlynecessary to observe an X-ray tube in action. It will be seen to bedivided into two hemispheres by the j^lane which contains the p itinumplate (see Fig. 475). The hemisphere which is facing the source of theX rays will be aglow with a greenish fluorescent light, while the otherhemisphere, being screened from the rays, is darker. By moving afluoroscope (a zinc-sulphide screen) about the tube it will be made evidentthat the rays which render the bones visible come from P. 440 INVISIBLE RADIATIONS 500. Nature of X rays. While X rays are like cathode raysin producing fluorescence, and

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bookidpracticalphysics00mill bookyear1922 bookdecade1920 bookcentury1900 bookauthormillikanrobertandrews bookauthorgalehenrygordon booksubjectphysics bookpublisherbostonginnandco bookcontributoruniversityofbritishcolumbialibrary booksponsoruniversityofbritishcolumbialibrary bookleafnumber504 bookcollectionubclibrary bookcollectiontoronto

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