. The principles and practice of roentgenological technique . nion the wedge-shaped piece ofaluminum is moved until the illumination ofthe windows over the metals is even. By meansof a small hood, placed over the windows, thismeasurement may be made in daylight. Thepointer indicates the degree of hardness meas-ured in Wehnelt units. secondary circuit, the plates and the pendulumare both equally charged, and the repulsionwhich is produced will be directly proportionalto the electrical tension in the circuit. Apointer attached to the pendulum passes overa suitably divided scale, the deviation de
. The principles and practice of roentgenological technique . nion the wedge-shaped piece ofaluminum is moved until the illumination ofthe windows over the metals is even. By meansof a small hood, placed over the windows, thismeasurement may be made in daylight. Thepointer indicates the degree of hardness meas-ured in Wehnelt units. secondary circuit, the plates and the pendulumare both equally charged, and the repulsionwhich is produced will be directly proportionalto the electrical tension in the circuit. Apointer attached to the pendulum passes overa suitably divided scale, the deviation depend-ing upon the voltage in the secondarycircuit. The instrument is suspended from abracket so as to be always in a vertical posi-tion. It is unipolar and may be connectedto the negative terminal of the coil or thecathode of the tube. The divisions on the scale correspond to thequality of the rays absorbed by lead of variousthicknesses. Thus, 1° on the scale correspondsto x-rays of such a hardness as to be totallyabsorbed by 1/10 millimeter of lead. \\hen. Fig. 138.—Walter Qualinieter, the index is at 10°, the tube should be emittingrays capable of penetrating 9/10 (.9) mm. oflead and be totally absorbed by 1 mm. of themetal. 2. By Measuring Penetrative Quality ofTHE Ray (a) Mcasurcincnt by Selective number of scales have been constructed,based on the selective absorption by metalsof rays of varying penetrability. Thus,silver and other metals whose atomic weightis about 100 do not absorb the rays of lowpenetrating power to any greater degree thanthe highly penetrating rays, while the absorp-tive power of aluminum varies with thequality of the rays, the soft rays being ab-sorbed more than the medium or hard. Thus by comparing the absorptive powerof lavers of aluminum to that of a certain BENOIST AND WALTER METERS 97 fixed thickness of silver, as judged by thefluorescent power of the emergent ray, adefinite scale may be constructed. Roentgen himself was the firs
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectradiogr, bookyear1920
