When the C-clef is placed on the third line of the stave, it is called the alto clef. As with all C-clefs, this line indicates the position of middle C.
Altostratus is a middle altitude cloud genus belonging to the stratiform physical category characterized by a generally uniform gray to bluish-gray sheet or layer, lighter in color than nimbostratus …
An old alchemical sign for alum or alumen.
A 17th century chemical sign for alum.