Hi William,

I went to Earliest Uses of Various Mathematical Symbols where Jeff Miller, a teacher at Gulf High School in New Port Richey, Florida has a wonderful collection of early uses of mathematical symbols. Under "Symbols of operation" he has

The obelus (÷) was first used as a division symbol by Johann Rahn (or Rhonius) (1622-1676) in 1659 in Teutsche Algebra (Cajori vol. 2, page 211).

I then looked up obelus in my Webster's New World Dictionary, second college edition, 1974 and I found

obelus: a mark (- or ÷) used in ancient manuscripts to indicate questionable passages or readings.