Pivotal coupling for instrument linkage

Claim 1

LINKAGE INCLUDING A FIRST LEVER AND A SECOND LEVER, EACH SAID LEVER HAVING ONE END THEREOF JOINED TO ONE END OF THE OTHER SO AS TO DEFINE A PIVOTAL COUPLING, SAID COUPLING INCLUDING A BALL AND A SOCKET, SAID BALL BEING RECEIVED IN SAID SOCKET; ONE SAID LEVER BEING DEFLECTIBLE IN A FIRST PLANE, AND THE OTHER SAID LEVER BEING DEFLECTIBLE SO AS TO HAVE A COMPONENT OF DEFLECTIONS IN A SECOND PLANE PARALLEL TO SAID FIRST PLANE; SAID BALL BEING FIXED TO THE SIDE OF SAID FIRST LEVER AT SAID ONE END THEREOF, AND SAID SOCKET BEING FIXED TO THE SIDE OF SAID SECOND LEVER AT THE SAID ONE END THEREOF; THE INSIDE OF SAID SOCKET HAVING THE FORM OF A SURFACE OF REVOLUTION, WHEREIN IN THE AXIS OF REVOLUTION LIES TRANSVERSE TO THE SAID PLANES, THE SAID INSIDE OF SAID SOCKET HAVING SUCH PROPORTIONS AS TO RECEIVE SAID BALL TO THE EXTENT OF A GREAT CIRCLE THEREOF, AND SAID BALL HAVING A GREAT CIRCLE IN SAID SOCKET, SAID GREAT CIRCLE LYING IN A PLANE NORMAL TO SAID AXIS OF REVOLUTION; MEANS PREVENTING SAID BALL FROM EMERGING FROM SAID SOCKET SO FAR AS TO ALLOW SAID GREAT CIRCLE TO LIE OUTSIDE SAID SOCKET; SAID FIRST LEVER HAVING A BEARING SURFACE ON THE SIDE THEREOF OPPOSITE TO ITS FIRST SAID SIDE, SAID SECOND LEVER HAVING A PORTION EXTENDING ALONG ITS SAID END AND SPACED THEREFROM, SAID PORTION HAVING A BEARING SURFACE ON THE SIDE THEREOF FACING THE SAID FIRST LEVER, THE TWO LAST SAID BEARING SURFACES BEING CONSTRUCTED AND ARRANGED TO MAKE BEARING CONTACT WITH EACH OTHER AT A SINGLE POINT SUBSTANTIALLY ON THE SAID AXIS OF REVOLUTION, WHEREBY TO DEFINE THE AFORESAID MEANS; THERE ALSO BEING PROVIDED MEANS BIASING SAID PORTION AND THE SAID ONE END OF SAID LEVER TOGETHER, AND THERE BEING PROVIDED FURTHER MEANS MAINTAINING SAID PORTION AND SAID ONE END OF SAID SECOND LEVER AT SUBSTANTIALLY JUST SUFFICIENT DISTANCE TO PREVENT SAID BALL FROM SHIFTING OUT OF SAID SOCKET SO FAR THAT THE SAID GREAT CIRCLE LIES OUTSIDE SAID SOCKET.