Practical podiatry : . machinemerely implies that the devices used for interrupting theprimary current have been eliminated. There is one other type of apparatus which is built onthe principle of an electrically oscillating system. Hereagain a start is made with the alternating current, obtainedeither from the line or by changing the direct current bymeans of an interrupter. The current is transformedthrough a so-called step-up transformer into one of highpotentiality which is then still alternating. This currentoscillates over a spark gap. Parallel to this spark gap ajesonator is connected ij
Practical podiatry : . machinemerely implies that the devices used for interrupting theprimary current have been eliminated. There is one other type of apparatus which is built onthe principle of an electrically oscillating system. Hereagain a start is made with the alternating current, obtainedeither from the line or by changing the direct current bymeans of an interrupter. The current is transformedthrough a so-called step-up transformer into one of highpotentiality which is then still alternating. This currentoscillates over a spark gap. Parallel to this spark gap ajesonator is connected iji which impulses are produced that X-RAYS IN PODIATRY 391 correspond to the discharges over the gap and which, ifapplied to a specially built, so-called high frequency Roent-gen ray tube, will produce X-rays. Since the principle ofelectric oscillations of a high frequency is used in this typeof apparatus, it is generally called the high frequencyRoentgen ray apparatus. Roentgen Ray Tubes. The various types of apparatus. TUNGSTEN TARGET TUBE previously described require special forms of Roentgenray tubes. For the coils by virtue of their relatively smallcapacity, platinum target tubes are generally capacity of the interrupterless type being considerablyhigher, the use of a material of greater resistance as a targetis necessitated. For this purpose tungsten is generallyemployed. For the high frequency, or Tesla coils, a tubewhich embodies a rectifying or valve action device is neces-sary. The mechanism of the production rays canbe described in the following way: the cathode, or negativeterminal of the tube, consists of a hollow spherical surfaceof aluminum. When this electrode is attached to a nega-tive potential, a stream of negative ions or cathode rays 392 PODIATRY is projected perpendicular to the surface of the reason of its curvature, the electrode is therefore focusedto produce a converging beam of cathode rays, the area ofwhich is sma
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