. Journal of radiology . bemade rapidly and accurately, weconstructed a crude electroscope,equipped with a reading micro-scope for observing the rate offall of the gold leaf, and con-nected to an ionization chamberby an enameled copper wire,which was insulated and sup-ported by paraffin and sulphurand enclosed in flexible metaltubing, ( Fig. 4). A series of measurements withthe ionization chamber at thesurface and at a depth of fourcentimeters in the phantomshowed a definite drop in theratio of the intensities at thesetwo points whenever the voltagewas raised, (Fig. 6). At the limitof the appa
. Journal of radiology . bemade rapidly and accurately, weconstructed a crude electroscope,equipped with a reading micro-scope for observing the rate offall of the gold leaf, and con-nected to an ionization chamberby an enameled copper wire,which was insulated and sup-ported by paraffin and sulphurand enclosed in flexible metaltubing, ( Fig. 4). A series of measurements withthe ionization chamber at thesurface and at a depth of fourcentimeters in the phantomshowed a definite drop in theratio of the intensities at thesetwo points whenever the voltagewas raised, (Fig. 6). At the limitof the apparatus, one hundredkilovolts measured with a spheregap, the ratio was about eightto one. Abandoning the lowervoltages as being less efficient,Ave made a second series of meas-urements at one hundred kilo-volts, using gradually increasingthicknesses of aluminum as fil-ters. The addition of each layerof aluminum was followed by afurther drop in the surface-depthratio, until, with a filter of tenmillimeters of aluminum, the. Figure V.—Photograph of measuring apparatus. 6 HOMOGENEOUS RADIATION OF THE CHEST—ERSKINE necessary ratio of four to onewas obtained, (Fig. 7). The foregoing measurementswere all made through a dia-phragm two centimeters squarein order to eliminate secondaryradiation. When the exposureswere made over an area six centi-meters square, the ratio was re-duced to three to one, (Fig. 3). When one-half millimeter ofcopper backed with a millimeterof aluminum was used in placeof the filter of ten millimeters ofaluminum, there was no materialdifference in the readings, (). i v Figure VI. The rate of discharge of theelectroscope with the ionizationchamber at a depth of four centi-meters in the paraffin phantom,was the same as when it wasplaced under two and one-halfcentimeters of water, (Fig. 3).This corresponds closely enoughto the thickness of the chest walls of the average sized womanof cancer age. The conclusions to be drawnfrom this series of observations ar
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