. Radiography and radio-therapeutics . taken not to use a current in the secondary exceeding 3 to 4 milliamperes. X-rays of sufficient hardness to penetrate the glass of the tube aregenerated only when the Electro Motive Force of the discharge has adefinite high value. With an induction coil this high EMF exists practicallyduring the time of the discharge; with the interrupterless alternatingtransformer the EMF has a sufficiently high value only during the shorttime the wave is near its height, the beginning and the end of the wavebeing of no great value for the production of X-rays of any deg
. Radiography and radio-therapeutics . taken not to use a current in the secondary exceeding 3 to 4 milliamperes. X-rays of sufficient hardness to penetrate the glass of the tube aregenerated only when the Electro Motive Force of the discharge has adefinite high value. With an induction coil this high EMF exists practicallyduring the time of the discharge; with the interrupterless alternatingtransformer the EMF has a sufficiently high value only during the shorttime the wave is near its height, the beginning and the end of the wavebeing of no great value for the production of X-rays of any degree ofpenetration, though they are still capable of influencing the milli-amperemeter ; they also produce heat which acts on the tube. Experiments carried out by W. E. Schall with the two types of apparatus,using the same number of milliamperes and the same length of exposure, 36 RADIOGRAPHY appear to show that the coil gives under the same conditions a greatervalue in penetrating rays. The accompanying figure illustrates this point:. A and B are positives from negatives obtained of an aluminium laddertaken with the same tube and the same number of milliampere-seconds. A was taken with a spark coil with 6 milliamperes and 12 seconds =72 milliampere-seconds. B was taken with an alternating transformer 6 milliamperes and 12seconds. The result in A is much better than in B.
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