Shabbat 157b (קנז:) — the Talmud in English

Rabbi Yehuda said that Rav said: There was a small

[path]

there

there,

between two houses. And there was ritual impurity

there on this path.

And a cracked vat was placed over the roofs

of the two houses. The corpse was lying beneath the place of the crack. However, it was not known whether the crack was an opening measuring a handbreadth or not. There was a window in the wall of the houses facing the path.

And it is established that if a corpse is lying in a tent in such a manner that the ritual impurity has no place to exit upward, it spreads into the houses alongside the tent through the hole in the wall [if the hole measures a fistful]. That was what occurred in this incident. The vat was roofing over the corpse and prevented its impurity from exiting upward. Therefore, the impurity was destined to enter the houses on either side of the path through the aperture [the window] in the wall and render everything inside them impure with the ritual impurity of a tent.

And

in order to prevent this, before the soul of the corpse departed,

they blocked the aperture

[the window in the wall]

with a tefiah

[an earthenware vessel], with its back facing the path where the corpse lay. Since an earthenware vessel does not become impure through its back, its back serves as a barrier against the ritual impurity.

After he died, they wanted to remove the tefiah from the window. But they were concerned that by doing so they would once again bring ritual impurity into the house. Therefore, they had to measure the size of the crack in the vat. If the crack measured a handbreadth, and the corpse was lying opposite it, the impurity would not spread to the sides. Rather, it would exit upward through that opening. But if the crack was less than an opening measuring a handbreadth, the impurity would not exit through it. And if the stopper were removed from the window, the impurity would enter the house.

Therefore, they took the mekidah [an earthenware vessel] that measured exactly one handbreadth by one handbreadth.

And they tied

it

the mekidah

to a long pole

with a reed.

They raised it opposite the crack to see whether it would enter it. From this it would be possible

to know whether there was there

in the crack

in the vat

a measure of

an opening measuring a handbreadth,

through which the impurity could exit, so that it would not enter the house,

or not.

They specifically tied it with a reed because it is fit for animal consumption and does not become functionally attached to the vessel, making the knot a permanent knot. For it will eventually be removed for the animal to eat.

Alternatively, it is not a permanent knot because when it dries, it becomes detached on its own. Rashi, according to the Rashash.

We learned in the Mishna:

And from their words we learned that one may block, measure, and tie on Shabbat.

Ulla happened to come to the house of the Exilarch. He saw Rabba bar Rav Huna sitting in a

vat

of water, and measuring

[measuring]

it

to determine the size of the vat.

He said to him: Say,

this

that the Sages said “

measure on Shabbat,” they said this only with regard to

measuring for a mitzva.

For example, for the laws of ritual impurity or for determining whether a ritual bath is valid. But with regard to measuring

that

is

not

for a

mitzva, who said

that it is permitted?

Rabba bar Rav Huna said to him:

I have no need whatsoever for this measurement.

I am merely occupying myself.

And they prohibited only measurement in which one has a practical need.

We have returned to you, chapter “One Whose Shabbat Eve Became Dark”

And tractate Shabbat is concluded