. American X-ray journal . d by gently tap-ping the tube. In air at ordinary atmospheric press-ure, the nearer the discharge points aretogether the more easily the spark takesplace between them ; that is to say, theshorter the distance the spark has toleap, the less is the difference of poten-tial required to make it leap. Curiouslyenough in high vacua the exact contraryis the case, and the discharge passeswith much greater difficulty over a shortgap than over a long one. This may bereadily seen with an adjustable tube suchas I will now show (Fig. 5), and inwhich I can alter the distance betwe
. American X-ray journal . d by gently tap-ping the tube. In air at ordinary atmospheric press-ure, the nearer the discharge points aretogether the more easily the spark takesplace between them ; that is to say, theshorter the distance the spark has toleap, the less is the difference of poten-tial required to make it leap. Curiouslyenough in high vacua the exact contraryis the case, and the discharge passeswith much greater difficulty over a shortgap than over a long one. This may bereadily seen with an adjustable tube suchas I will now show (Fig. 5), and inwhich I can alter the distance betweencathode and anticathode by moving thelatter. As will be seen when the dis-tance is very small inside the tube, sayonly one-quarter of an inch, the spark prefers the alternative gap outside ofabout four inches, while if the internalgap is increased to about three inches,the discharge then prefers this path,and the exterior gap must now be short-ened to about half an inch before thespark will travel that way. It is further. fig. 5. found that, in a tube of this description,exhausted to a constant vacuum, thenearer the anticathode is moved up tothe cathode and the higher the conse-quent resistance, the more penetrative arethe x-rays; while moving the anti-cathodein the opposite direction, and thus mak-ing the distance greater and the resist-ance less, makes the x-rays less pene-trative. This form of tube was the firstadjustable tube designed and made in
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectrad, booksubjectxrays
