Siman - Eruvin Daf 45
- When a Jewish city is under siege by nochrim
Rav Yehudah said in the name of Rav, נכרים שצרו על עיירות ישראל – if nochrim besieged a Jewish city on Shabbos, אין יוצאין עליהם בכלי זיינן – Jews may not go out against them with weapons, ואין מחללין עליהן את השבת – nor may they violate Shabbos because of them. A Baraisa stating the same, further clarified that this rule was only said, על עסקי ממון – where the nochrim came over a money matter, meaning where there was only a threat to property, אבל באו על עסקי נפשות – but if they came over a matter of lives, meaning where people’s lives are being threatened, they may go out against them with their weapons and be mechallel Shabbos. ובעיר הסמוכה לספר – And in a case of an attack on a border city, even if the nochrim only came over a matter of straw and stubble, which are not worth much, Jews may go out against them with weapons and be mechallel Shabbos. The reason is that the capture of a border city by the enemy would expose the interior of the country to invasion.
- Someone sleeping on the journey and did not know it had become dark
The second Mishnah on the Daf states, מי שישן בדרך ולא ידע שחשכה – Someone who fell asleep on a journey and was not aware that it had become dark, and he did not have in mind to acquire a techum, Rebbe Yochanan ben Nuri says that he has two thousand amos in every direction from his location, whereas the Chochomin say that he only has four amos.
Rav Yosef proves from a Baraisa that Rebbe Yochanan ben Nuri holds, חפצי הפקר קונין שביתה – ownerless objects acquire a Shabbos residence and may not be moved beyond the techum, and therefore a sleeping person as well acquires a makom shevisa from which to measure a techum. The Baraisa stated that if rain fell on erev Yom Tov, and was ownerless when Yom Tov began, it has a fixed techum of two thousand amos in each direction. This must reflect the opinion of Rebbe Yochanan ben Nuri since Chochomim hold that one who falls asleep before Shabbos only has four amos.
Rain does not acquire its makom shevisa in the clouds
The Baraisa that Rav Yosef brought also stated that if rain fell on Yom Tov, הרי הן כרגלי כל אדם – it is treated like the feet of anyone who eventually owns it, meaning it has their techum. The Gemara asks, ליקני שביתה באוקיינוס – let the waters acquire their shevisa in the ocean, since it was there at the start of Yom Tov, and Rebbe Yitzchak answers that the water was already in clouds that had gathered before Yom Tov. The Gemara goes on to explain that the reason that the water does not acquire its makom shevisa in the clouds and receive a techum area there is, מיא בעבים מינד ניידי – the water in the clouds is constantly in motion, and therefore does not receive a techum limit until it comes to a halt.
