System for elevating building components

Claim 1

IN A LIFTING STRUCTURE, THE COMBINATION OF A JACK UNIT PROVIDED WITH AN UPPER AND A LOWER HEAD; MEAND SUPPORTING THE LOWER HEAD; A PAIR OF SPACED, UPRIGHT SCREWS EXTENDING THROUGH THE HEADS AND COUPLED WITH A LOAD TO BE LIFTED; POWER MEAND BETWEEN THE HEADS HAVING VERTICALLY RECIPROCABLE MEAND FOR RAISING THE UPPER HEAD; A PAIR OF UPPER NUTS, ONE ON EACH SCREW RESPECTIVELY ABOVE THE UPPER HEAD, THROUGH WHICH THE SCREWS AND LOAD ARE LIFTED WHILE THE UPPER HEAD IS RAISED; A PAIR OF LOWER NUTS, ONE ON EACH SCREW RESPECTIVELY ABOVE THE LOWER HEAD, THROUGH WHICH THE LATTER SUPPORTS THE SCREWS AND LOAD WHILE THE UPPER HEAD DESCENDS; A FIRST MECHANISM CONNECTED WITH THE LOWER NUTS FOR LOWERING THE LATTER FOLLOWING THE COMMENCEMENT OF EACH STEP OF ASCENT OF THE UPPER HEAD; A SECOND MECHANISM CONNECTED WITH THE UPPER NUTS FOR LOWERING THE LATTER FOLLOWING THE COMMENCEMENT OF EACH STEP OF DESCENT OF THE UPPER HEAD; A PRIME MOVER FOR ACTUATING SAID MECHANISMS, SAID PRIME MOVER BEING PROVIDED WITH A DRIVE MOVABLE ALTERNATELY IN OPPOSITE DIRECTIONS; APPARATUS COUPLING THE DRIVE WITH THE FIRST MECHANISM FOR ACTUATING THE LATTER WHEN THE DRIVE MOVES IN ONE DIRECTION; AND APPARATUS COUPLING THE DRIVE WITH THE SECOND MECHANISM FOR ACTUATING THE LATTER WHEN THE DRIVE MOVES IN THE OPPOSITE DIRECTION.