File:The Röntgen rays in medical work (1899) (14570246609).jpg

Identifier: rntgenraysinmedi00wals (find matches)
Title: The Röntgen rays in medical work
Year: 1899 (1890s)
Authors: Walsh, David
Subjects: X-rays Radiography X-Rays Radiography
Publisher: London : Baillière, Tindall and Cox
Contributing Library: Francis A. Countway Library of Medicine
Digitizing Sponsor: Open Knowledge Commons and Harvard Medical School

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hat make a good tube, so that another like it can be pro-duced at will, although, on the other hand, the excellences of atube, its definition and penetration, can always be tested before ELECTRICAL APPARATUS AND METHODS 41 purchase. The resistance should be proportioned to the size ofthe coil, and if wished can be reduced for a time, either byheating the tube with a spirit lamp or by reversing the currentfor a few moments. Mr. A. A. Campbell Swintons adjustablefocus tube is devised upon a sound principle, and one can onlywonder why it has not come into more general use amongpractical workers. He has shown that the kathodal rays areprojected from the aluminium cup-shaped anode in a hollowcone merging into a beam that strikes the anti-kathode. By asliding kathode (which may be adjusted by Dawson Turnersmethod from outside by a magnet) he regulates the distancebetween kathode and anti-kathode, so that the tube may beindependent of alterations of resistance, and be fitted for various V^S.
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Fig. 20. kinds of work. An excellent tube for high-resistance coils andfor deep tissues is the Penetrator of Messrs. Watson and Co. There yet remain two methods of reducing the resistance in atube. The first, by heating some substance contained in an annex,such as potash or palladium, whereby the vacuum is lowered.One of the latest types of this kind is the Queen tube, whichis so arranged that when the tube resistance reaches a certainpoint, the current passes by an alternative route into a communi-cating potash bulb, whereby vapour is driven off and the vacuumof the main tube lowered, so that it is again brought into action.This result depends on the fact that some free gaseous moleculesare needed to form a path for the electrical current; but thoseleft in the original state of the tube appear to become graduallyoccluded, and are set free again by the heat. The other method alluded to depends on the theory that theouter side of a focus-tube in action becomes inductively chargedwith e

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