. Archives of physical medicine and rehabilitation . through careful studyby Victor engineers of all the factorsinvolved, and extensive experimentalwork, reverting to the conditions underwhich the radiographs are produced, todetermine their exact relation to amethod for producing correct stereo-vision. A radical departure is made fromstereoscopes of previous design, in thatonly one light bulb is used in each view-ing box instead of the usual four. Thissingle 150 watt bulb, nitrogen filledand with a concentrated tungsten fila-ment, is placed centrally in the viewingbox. From the fact that the d
. Archives of physical medicine and rehabilitation . through careful studyby Victor engineers of all the factorsinvolved, and extensive experimentalwork, reverting to the conditions underwhich the radiographs are produced, todetermine their exact relation to amethod for producing correct stereo-vision. A radical departure is made fromstereoscopes of previous design, in thatonly one light bulb is used in each view-ing box instead of the usual four. Thissingle 150 watt bulb, nitrogen filledand with a concentrated tungsten fila-ment, is placed centrally in the viewingbox. From the fact that the distributionof light from this bulb corresponds veryclosely to the distribution of x-rays un-der which the radiograph is produced,that IS, with the intensity greater at thecentral portion of the film and wherethe anatomic part under study is usuallyplaced, this reproduction of conditionsobviously gives the natural effect or truestereovision. Compare this with the unequal dis-tribution of illumination characteristicof the four-bulb viewing box. With. four sources of illumination there arefour points of concentration, and, asthe bulbs may vary in efficiency theeffect would make diagnosis difficult,considering the composite nature ofsome radiographs. Then again, the usual practice ofplacing a separate control for each view-ing box has been abandoned in the de-sign of the Truvision a central rheostat control isused, with which the operator changesthe intensity of illumination in the boxessimultaneously; each negative is there-fore equally illuminated. A simple ex-periment will show that two sources ofillumination unequal in intensity appearto the observer as though in differentplanes, which effect can be varied byincreasing or decreasing the light in-tensity in either source. Logically, then,to avoid this in stereoscopy the illumina-tion in the viewing boxes must be ofequal intensity at all times. This isprovided for in the Truvision stereo-scope with (he central
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Keywords: ., bookauthoramerican, bookcentury1900, bookdecade1920, bookyear1920
