[Avodah] The size of a kazayit and of an amma

[Micha Berger]

On Mon, Mar 26, 2018 at 01:04:17PM +0200, Arie Folger via Avodah wrote:
: Now all shiurim are somehow connected with one another, weight, volume and
: length, are they? Hence, if our kezeitim and reviiyot are too large and
: should be smaller, so should the amma. IIUC, a reviit of 75cc corresponds
: to an amma of roughly 43.5-45cm.

Funny you should mention that, because I had a half-written email to Avodah
on the subject that I think evaporated before sent. (I think I accidentally
deleted it shutting down for Shabbos.)

A revi'is is 2 x 2 x 2.7 cubic etzba'os (Pesachim 109a, but see Y-mi
Sheqalim 3:2 [vilna 13b, bavli 9a], see Tosafos ad loc, "revi'is" giving
two explanations of the Y-mi both of which mean ruling like the Babli).
So, the weight of a durham, and knowing whether we map weight of a
revi'is of water of odf wine would allow us to compute an ammah.

RCN's 86cc instead of 75cc revi'is is an error in volume of 1.1467, or an
error in length of the cube root of that -- 1.047. So, RCN's ammah would
be corrected from 48cm to 45.9cm.

The Rambam implies the 75cc revi'is, as the Rambam says a revi'is [of
water? wine?] weighs the same as 27 dirham (Edios 1:2) -- the math RCN was
trying to do but with problems getting the right dirham. And... Shitas
haRambam (acc to Midos veShiurei Torah, R Chaim Benish) is 45.59-46.08cm
So I think I did the right math.

I think that RCN in theory holds like the Rambam, but had that error
in his metzi'us.

And I think that RCN was trying to justify the minhag of the Yishuv haYashan
and only came in too high because of that error. IOW, it seems to me that
the YhY of his day was simply following the Rambam, whether they realized
that's what they were doing, or de facto, doing what everyone sees done was
the Rambam's shitah.

I do not know how you got the range you did, but that's how the inyan looks
to me. Still might be an eiruv problem, as far as I know.


When I tried to use archology to get historical ammos, I raised the
question of whether kelalei hapesaq mean that the historal shiur needn't
be the same as the current one. Or that the ammah in Chizqoyahu's day
needn't be the same as those found in bayis sheini.
<http://www.aishdas.org/asp/units-of-measure> (Which I believe includes
Zev's corrections of my math.)

Tir'u baTov!
-Micha

-- 
Micha Berger             The goal isn't to live forever,
micha at aishdas.org        the goal is to create so mething that will.
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