§ 6. Call of the Senate. For the purpose of securing the attendance of
Senators, a call of the Senate may be ordered at any time, but such call
shall  not  be  in order after the voting on any question has begun, nor
after the third reading of a bill has  been  completed,  nor  after  the
motion  to  close  debate  has been ordered pursuant to section three of
this Rule, unless it shall appear upon an actual count by the  Presiding
Officer that a quorum is not present.