Specific gravity or flow indicator

Claim 1

IN A FORCE-MEASURING DEVICE OF THE CHARACTER DESCRIBED, A CONDUIT MEMBER, A MAGNETIC MEMBER MOVABLYY DISPOSED IN SAID CONDUIT MEMBER, FLUID IN SAID CONDUIT MEMBER EXERTING FORCE ON SAID MAGNETIC MEMBER, A COIL WOUND ON SAID CONDUIT MEMBER, A SOURCE OF CURRENT, A PHOTO CELL ON ONE SIDE OF THE CONDUIT MEMBER, A LIGHT SOURCE ON THE OTHER SIDE OF THE CONDUIT MEMBER, MEANS PROVIDING A LIGHT-TRANSMITTING PATH BETWEEN SAID LIGHT SOURCE AND PHOTO CELL, SAID MAGNETIC MEMBER BEING AT LEAST PARTLY IN SAID PATH, WHEREBY TO VARY THE AMOUNT OF LIGHT IMPINGING ON THE PHOTO CELL IN ACCORDANCE WITH MOVEMENTS OF THE MAGNETIC MEMBER RELATIVE TO SAID COIL, A MASKING PLATE MOUNTED BETWEEN SAID CONDUIT MEMBER AND SAID PHOTO CELL AND HAVING A LIGHT-TRANSMITTING APERTURE IN SAID LIGHT-TRANSMITTING PATH, SAID APERTURE BEING OF VARYING WIDTH IN THE DIRECTION OF MOVEMENT OF SAID MOVEMENT OF SAID MAGNETIC MEMBER IN SAID CONDUIT MEMBER, WHEREBY TO CORRESPONDINGLY VARY THE SENSITIVITY OF RESPONSE OF SAID PHOTO CELL, A SOURCE OF CURRENT, CURRENT CONTROL MEANS, MEANS OPERATIVELY CONNECTING SAID PHOTO CELL TO SAID CURRENT CONTROL MEANS, CIRCUIT MEANS CONNECTING SAID SOURCE TO SAID COIL THROUGH SAID CURRENT CONTROL MEANS, WHEREBY TO PRODUCE A FLOW OF CURRENT THROUGH THE COIL WHICH STAB LIZES AT A VALUE SUFFICIENT TO PROVIDE A MAGNETIC FORCE ON THE MAGNETIC MEMBER BALANCING THE FLUID FORCE ACTING THEREON, AND MEANS TO MEASURE SAID CURRENT.