Talmud for Eruvin 115:13
תנינא להא דתנו רבנן היה מודד והגיע המידה לגיא אם יכול להבליעו בחבל של חמשים אמה מבליעו ואם לאו הולך למקום שיכול להבליעו ומבליעו וצופה וחוזר למידתו
from where<span class="x" onmousemove="('comment',' The width across being less than fifty cubits.');"><sup>24</sup></span> he is able to do so and, after spanning it, he makes the necessary observations<span class="x" onmousemove="('comment',' Lit., , 'and looks'.');"><sup>25</sup></span> [whereby he is enabled to locate the point on the far side]<span class="x" onmousemove="('comment',' Of the obstruction that could not be spanned.');"><sup>26</sup></span>
Jerusalem Talmud Eruvin
HALAKHAH: Paragraph. “One only measures with a rope of 50 cubits,” etc. How much is the measure of the Sabbath domain? 40 ropes. “Neither less” since it can be tightened and increases, “nor more” since it gets loose and loses116Babli 58 a.. Some Tannaim state, one measures with a linen rope, but some Tannaim state, with a chain rope117A metal chain., and some Tannaim state, with a rope of four cubits. 116Babli 58 a. Rebbi Joshua said, there is no truer measure than with chains, but what can I do since in Prophets it is written ropes, a linen twine was in his hand and a measuring rod118Ez. 40:3..
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