. The Roentgen rays in medicine and surgery as an aid in diagnosis and as a therapeutic agent : designed for the use of practitioners and students . Fig. 29. Details of rotary target. Full size. (Rollins.)The rotary target is liable to be turned somewhat on its pivot if the tube is transported some dis-tance, and as the effect of exposing a new surface to the impact of the cathode stream may be to lower theresistance of the tube (see page 45), a tube of this type should be examined by the practitioner beforeit is used, in order that he may learn whether or not the target has been so shaken tha
. The Roentgen rays in medicine and surgery as an aid in diagnosis and as a therapeutic agent : designed for the use of practitioners and students . Fig. 29. Details of rotary target. Full size. (Rollins.)The rotary target is liable to be turned somewhat on its pivot if the tube is transported some dis-tance, and as the effect of exposing a new surface to the impact of the cathode stream may be to lower theresistance of the tube (see page 45), a tube of this type should be examined by the practitioner beforeit is used, in order that he may learn whether or not the target has been so shaken that it has turnedon its pivot. This point can be determined by observing whether or not the spot that has beenrout^hened by the impact of the cathode stream is in Ime with the centre of the cathode; if not, itmust be shaken into line. The following figure illustrates a not uncommon form of construction,which is faulty, in that the target is in the centre of curvature of thecathode disk, and that the wrappings of the stem are of glass, which areliable to break both in use and in transportation, with the result that theterminals get out of Fig. 30. Tube of a faulty type of construction. Target in centre of curvature of cathode; wrap-pings of stem are of glass. Double Focus Tubes for Use with an Alternating Current. — With thepowerful currents that may be used with high frequency coils, holes areHable to be melted in the target by the heat produced by the impact ofthe cathode stream, and the tubes be rendered useless. To overcomethis defect. Dr. Rollins has designed double focus tubes containingeither his cooled or rotary target. A second objection to the doublefocus tubes is that they have two sources from which the X-rays origi-nate (see Fig. 32); the definition, therefore, is not so good as it may bewith a single focus tube. To obviate this objection to the use of alternat-ing currents, Dr. Rollins has designed the tubes shown in Figs. 33-35 —one the cooled target type
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