749. Things That Can Substitute for a Corner

Shabbos 17:28

If one of the corners around a well - or even all four corners -  has a large rock, a tree, a mound that slopes to higher than ten handbreadths (30”) within four cubits (6’), or a bundle of reeds, then we determine whether this item has an area one cubit long (about 18”) and ten handbreadths high on either side. If it does, we treat it the same as two perpendicular walls. If five reeds are erected and there’s less than three handbreadths (about 9”) between each reed and the next, the gaps between them are considered closed up. If there are six handbreadths on each side, they are considered like two perpendicular walls.

Shabbos 17:29

One is permitted to move these four corners closer to the well as long as there is still enough room for the greater part of a cow's body to fit within the walls while drinking from the well. Even though one does not hold the head of an animal and the vessel that holds the water, since there is room for the cow’s head and the greater part of its body, this is permitted. If the enclosure is this size, even a camel (which is larger than a cow) can use the well. If the enclosure is smaller, one may not draw water even for a kid, which would fit entirely within the enclosure. The walls may be moved as far from the well as one likes so long as he continues to add straight sections to the walls on each side so that there is never a gap of more than 13 1/3 cubits (about 20’) between walls.