This was what has since become the fourth line, the clef line, of the bass stave.
After a change of clef in the middle of a score this is, of course, not necessary.
She was so tall the girls always considered her in that clef.
They could only be written (as they are yet) in one clef—namely, the F clef.
Clef, klef, n. a musical character placed on the staff by which the absolute ...