Subject: Re: [HM] symbol for infinity
From: John Conway (conway@math.Princeton.edu)
Date: Mon Jan 03 2000 - 10:49:51 EST
On Sun, 2 Jan 2000, Eric Detrez wrote:
> I'm looking for the origin of the symbol for infinity (oo).
> Who introduced this notation? And is there any signification?
>
Menninger's "Number Words and Number Symbols" says it is
derived from the original form of the Roman Numeral M for 1000,
which was an Etruscan letter whose sides were curved - let me
try to draw it as well as I can:
_ _
( | )
Half of this, namely
_
| )
is said to have given rise to D for 500, in much the same way
that half of X gives V and half the original form of C :
__
|
|__
is supposed to have given L, though to me this all sounds a bit
too neat to be true.
By doubling the arms thus:
_ _ _ _
( ( | ) )
one got a symbol for 10,000, and apparently people were in the
habit of using these symbols loosely for any very large numbers,
in much the same was as we say "billions". Gradually the symbol
was simplified to become the modern "infinity" sign.
I advise you to consult Menninger's book for yourself, since
I have to warn you that I'm writing from memory as usual.
John Conway
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