Optical instrument with liquid mirror for locating ground point vertically aligned with overhead sighting point

Claim 1

AN OPTICAL DEVICE SUITED FOR SIGHTING A POINT LOCATED ABOVE THE DEVICE AND FOR MARKING ON THE GROUND THE VERTICAL PROJECTION OF THE SIGNED POINT COMPRISING: A BASE ADPATED TO BE SUPPORTED WITH RESPECT TO THE GROUND, A CASING SUPPORTED BY SAID BASE AND CONTAINING OPTICAL ELEMENTS, A RETICULE MOUNTED IN A VERTICAL CHANNEL WITHIN SAID CASING, SAID RETICULE DETERMINING A REFERENCE POINT, A RECEPTACLE SUPPORTED BENEATH SAID RETICULE BY SAID BASE AND CONTAINING A LIQUID, THE FREE SURFACE OF WHICH CONSTITUTES A HORIZONTAL PLANE MIRROR, AN ABJECTIVE MOUNTED WITHIN SAID VERTICAL CHANNEL UNDER AN UPWARDLY FACING OPENING OF SAID CASING AND ABOVE SAID RECEPTACLE TO PROVIDE AN IMAGE OF THE SIGHTED POINT WHEN SAID OPENING IS POSITIONED SUBSTANTIALLY UNDER THE SIGHTED POINT WHILE SAID PLANE MIRROR GIVES A REFLECTED IMAGE OF SAID FIRST-NAMED IMAGE, MEANS FOR VARYING THE SPACING BETWEEN SAID OBJECTIVE AND SAID RECEPTACLE SO THAT THE REFLECTED IMAGE IS SUBSTANTIALLY IN THE HORIZONTAL PLANE OF SAID REFERENCE POINT, A SIGHTING ASSEMBLY SUPPORTED BY SAID BASE AND INCLUDING AN OBLIQUE PARTIAL-MIRROR MOUNTED WITHIN SAID CASING ABOVE SAID RETICULE AND SAID OBJECTIVE TO PERMIT OBSERVATION THROUGH SAID SIGHTING ASSEMBLY OF SAID REFERENCE POINT AND THE REFLECTED IMAGE. AND MARKING MEANS ATTACHED TO SAID BASE AND POSITIONED BENEATH SAID RECEPTACLE, SAID MARKING MEANS INCLUDING MEANS FOR MARKING ON THE GROUND A TRACE OF THE VERTICAL OPTICAL AXIS DETERMINED BY SAID REFERENCE POINT AND ITS IMAGE BY REFLECTION ON SAID PLANE MIRROR, THE TRACE CORRESPONDING TO THE VERTICAL PROJECTION OF THE SIGHTED POINT WHEN SAID DEVICE IS MOVED LATERALLY SO AS TO CAUSE THE REFLECTED IMAGE OF THE SIGHTED POINT TO COINCIDE WITH SAID REFERENCE POINT.