Etymology of "Rx"

[MARYPROTO at AOL.COM]

I edit a newsletter called Copy Editor, and one of our columnists has
submitted an article in which he writes:

"What about the origin of 'Rx'? It may have been an abbreviation of the Latin
_recipe,_ meaning 'take,' or a representation of the sign for Jupiter, which
'Rx' vaguely resembles. The sign on ancient prescriptions invoked the deity's
blessing on the medicine."

Every dictionary I've checked gives only the Latin "recipe" in the etymology
of "Rx" (if the dictionary lists "Rx" at all). I told the writer, who then
faxed me an article from FDA Consumer Magazine, which says:

"Where does the 'Rx' for 'prescriptions' come from? Its origins are given
variously as an abbreviation of the Latin word 'recipe,' meaning 'take,' or
as a representation of the astrological sign of Jupiter [SIGN HERE]. This
sign was placed on ancient prescriptions to invoke that deity's blessing on
the medicine to help the person get well. More recently, the cross at the end
of the 'R' has been explained as a substitute period."

I'm suspicious of the Jupiter connection, not only because of the source of
the information but also because the planet's sign looks nothing like "Rx."
Can anybody set the record straight for me? Many thanks.

Mary Beth Protomastro
Editor and Publisher
Copy Editor: Language News for the Publishing Profession
marybeth at copyeditor.com or maryproto at aol.com
http://www.copyeditor.com