Reference for Gittin 156:18
אמאי הא כי נפיל בארבע אמות דידה קא נפיל בדלא נח
and he threw it to her, even if the Get reached her hand she is not divorced. Why so? When it falls to the ground it falls within four cubits of her? — We assume that it does not come to rest there. But should she not be divorced by dint of its having come into the air of the four cubits? [And since this is not so] may we decide from this the question raised by R. Eleazar, whether the four cubits spoken of include the air above them or not? May we decide that they do not include the air? — [No;] we suppose here that she is standing on the brink of a river, so that from the outset it is liable to be lost [if it falls from her hand].<span class="x" onmousemove="('comment',' And in such a case the air certainly does not confer possession. ');"><sup>15</sup></span>