[Avodah] Shiur of an Etzbah(finger)

[Micha Berger]

On Mon, Feb 11, 2013 at 10:09:45AM -0500, Zev Sero wrote:
> The Rambam gave the shiur of a revi'is as 27 dirhams, by which he presumably
> meant the Egyptian ones of his day.  But the minhag Y'm, which RACN defended,
> was based on the Ottoman dirham, which was about 15% bigger than the Egyptian
> one that the Rambam knew, and thus all their shiurim were actually bigger
> than the Rambam's, though they probably didn't realise it.  The Rambam's
> etzba was thus approximately 19.1 mm rather than the 20 that RACN gives.

Which, as I noted in the past, would make the 1,200 amos that the length
of Chizqiyahu's Tunnel was given as on the inscription in shiloach
<http://en.wikipedia.org/wiki/Siloam_Inscription>
    1200 * 24 * 19.1 = 550 m
The tunnel is actually 533m, but presumably 1,200 is rounded. This is
an error of only 3%, perfectly normal if rounding to the nearest hundred
(2 digit precision), and the closest possible hundreds to round to.

Whereas, if we use RCN's measure, the tunnel's length would have been
rounded down to 1,100 amos (528m, only 5m less -- <1% difference) rather
than 1,200 (576m / 8%).

IOW, based on the water tunnel, all of the common shitos for ammah are
too long, but the Rambam's -- assuming you know that the Ottomans did
let the dirham drift in size -- is plausible.

I made a similar case based on distances between markings on Har haBayis
that recur in multiples of 43.5 +/- 2mm, that imply a given ammah. Or
a given ammah plus 1/2 etzba safety (Pesachim 86a). But that's only a
1.8 mm etzba (a shade above or less, depending on whether the marking
reflect the extra half-etzba). And also only if the markings are really
as old as Bayis Sheini.

-Micha

-- 
Micha Berger             "'When Adar enters, we increase our joy'
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