Amerikanische Röntgenzeitschrift (1897) (14570249539)

Identifier: americanxrayjour1418unse (find matches)
Title: American X-ray journal
Year: 1899 (1890s)
Authors:
Subjects: X-Rays Radiography
Publisher: St. Louis : American X-Ray Publishing Co.
Contributing Library: The College of Physicians of Philadelphia Historical Medical Library
Digitizing Sponsor: Open Knowledge Commons and the National Endowment for the Humanities



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falla-cy of this, and I now print a cut of oneof the perforated cathodes I have used in my experiments. A glance at Fig. 31will show that it has a solid center aslarge as the average cathode, and a wide,solid rim. If only the edges or centerof a cathode were active, this one shouldbe as efficient as though it was solid, butit is not. The cathode stream from it isso broken up and so little delivered atthe proper point on the target that thisis not made red hot by a current whichwould melt it with a solid cathode of thesame size. The appearances of perfo-rated cathodes of different designs arevery beautiful, as are the figures theyform on the glass walls, and both areworth careful study. NO. XXXIV—ON THE FALLACY OF USING THEEQUIVALENT AIR SPARK AS A MEASURE OFTHE DEGREE OF VACUUM IN A ROENT-GEN LIGHT TUBE. In the writings of men interested invacuum tubes it is not unusual to findthe degree of vacuum in a Roentgenlight tube measured by the equivalentspark in air. That other data should
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Fig. 33. accompany this statement is shown bythe following experiments. If we keepthe temperature of the water at 30 de-grees centigrade, in a tube like thatshown in Figure 30, Note XXX, andpump the vacuum until the resistance isequal to nine inches of air, when the tubeis excited on a large static machine, weshall find on exciting it with a Lawrenceand Norton coil and a 20-microfarad con-denser, that the equivalent spark in airis much less, usup^^l^p^^liijee^n^^s^If we now excite thetubeon an alternat-ing- currr&ni^Jy MMvj kthfeJ OF PHILADELPHIA 400 THE AMERICAN X-RAY JOURNAL. equivalent spark in air will be still less.Even with different types of inductioncoils, the equivalent air spark varies,depending on the mode of winding. Asextended description of experiments isout of place in these short notes, I saybriefly that at the degree of exhaustionrequired to produce Roentgen light, theresistance of the tube, as measured bythe equivalent spark in air, is inverselyas the voltage ; t