. American X-ray journal . ve amperes of cur-rent in an ordinary coil causes an E. capable of bridging an air gap ofabout one inch. With the interrupter incircuit the spark will jump six difference is due to the greater rap-idity by which the interrupter breaks thecurrent. Assuming that the E. M. F. isproportional to the spark length whichis very nearly true for lengths above oneinch, the time consumed in breaking-would be about 5 0 0 * e = tcW sec-onds. The breaks take place only whenthe current is passing from the platinumpoint to the lead plate. This accountsfor the polar ef
. American X-ray journal . ve amperes of cur-rent in an ordinary coil causes an E. capable of bridging an air gap ofabout one inch. With the interrupter incircuit the spark will jump six difference is due to the greater rap-idity by which the interrupter breaks thecurrent. Assuming that the E. M. F. isproportional to the spark length whichis very nearly true for lengths above oneinch, the time consumed in breaking-would be about 5 0 0 * e = tcW sec-onds. The breaks take place only whenthe current is passing from the platinumpoint to the lead plate. This accountsfor the polar efleets, as the E. M. F. gen-crated by the regular alternation of the 658 THE AM ERIC AX X-RAY JOURNAL current is not sufficient to bridge the airgap or pass through the tube. If, how-ever, the discharge rods be gradually ap-proached to within about one inch theusual discharge will be succeeded bv analternating high tension arc. the E. generated being then sufficient inboth directions to force the currentacross the Fig. 2. The radiograph of the fish was takenwith the alternating current and a sin-gle focus tube. Tt certainly shows asgood definition as can be obtained withdirect current excitation. No operator of an induction coil wholias access to a commercial circuit, eitheralternating or direct, of any voltage notexceeding 250 should fail to try thismethod. The cost of the apparatus issmall, and the results obtained will bewell worth the trouble. Sept. 25, 1S99. Restoring Impaired Screens. Mr. W. S. Andrews, of Schenectady,X. Y., lias kindly offered to restore im-paired screens that are unvarnished. Flu-oroscopes and open screens, after long-use, careless handling or when exposedto artificial heat, become dull and screens lose their former de-gree of fluorescence and do not muchchange in color. All such screens will gladly receive for treat-ment. It will pay those in possession ofsuch screens to correspond with Mr. An-drews. Re=Enforcing Sc
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