Measurement of fingerprint density apparatus and method

Claim 1

APPARATUS FOR MEASURING THE DENSITY OF A FINGERPRINT CARRIED BY A STRIP OF TRANSLUCENT MATERIAL HAVING A CLEAR AREA AND A FINGERPRINT AREA, SAID APPARATUS COMPRISING A SOURCE OF LUMINOUS ENERGY, MEANS FOR HOLDING SAID STRIP FOR ILLUMINATION BY SAID SOURCE EQUALLY ON SAID FINGERPRINT AREA AND SAID CLEAR AREA, FIRST AND SECOND PHOTOCONDUCTIVE ELEMENTS, MEANS DEFINING A FIRST LIGHT PATH BETWEEN SAID SOURCE AND SAID FIRST PHOTOCONDUCTIVE ELEMENT, SAID FIRST PATH PASSING THROUGH THE FINGERPRINT AREA OF SAID STRIP, MEANS DEFINING A SECOND LIGHT PATH BETWEEN SAID SOURCE AND SAID SECOND PHOTOCONDUCTIVE ELEMENT, SAID SECOND PATH PASSING THROUGH SAID CLEAR AREA OF SAID STRIP, SAID LIGHT PATHS BEING EQUALLY UNOBSTRUCTED IN THE ABSENCE OF A STRIP, A RESISTANCE BRIDGE CIRCUIT HAVING FOUR ARMS ONE OF WHICH INCLUDES SAID FIRST PHOTOCONDUCTIVE ELEMENT AND ANOTHER OF WHICH INCLUDES SAID SECOND PHOTOCONDUCTIVE ELEMENT, CALIBRATED INDICATING MEANS FOR INDICATING THE DEGREE OF UNBALANCE OF SAID BRIDGE, MEANS FOR BALANCING SAID BRIDGE WHEN SAID PHOTOCONDUCTIVE ELEMENTS ARE EQUALLY ILLUMINATED, A SHUTTER BLADE PIVOTALLY MOUNTED ADJACENT ONE OF SAID PHOTOCONDUCTIVE ELEMENTS FOR SELECTIVELY BLOCKING SAID FIRST PATH, A MANUALLY OPERABLE MEMBER EXTENDING FROM SAID APPARATUS FOR MOVING SAID SHUTTER