Reference for Eruvin 115:16
אמר רב יהודה אמר שמואל לא שנו אלא שאין חוט המשקולת יורד כנגדו
it is pierced in an upward, as well as in a downward direction.<span class="x" onmousemove="('comment',' The method of piercing is described infra 58b.');"><sup>29</sup></span> If it<span class="x" onmousemove="('comment',' The measuring line. iht');"><sup>30</sup></span> reached a wall we do not say: 'Let the wall be bored through';<span class="x" onmousemove="('comment',' Sc. that poles towering above it shall be held up on both its sides and the rope stretched from one to the other (Tosaf. s.v. a.l.) .');"><sup>31</sup></span> its thickness rather is estimated and the measuring continues.<span class="x" onmousemove="('comment',' Tosef. 'Er. IV.');"><sup>32</sup></span> Have we not, however, learnt: HE SPANS IT AND RESUMES HIS MEASURING?<span class="x" onmousemove="('comment',' Why then is a mere estimate allowed in this case?');"><sup>33</sup></span> - There<span class="x" onmousemove="('comment',' In our MISHNAH:');"><sup>34</sup></span> it is a case of one that can be conveniently used<span class="x" onmousemove="('comment',' One for instance that rises gently to a height of ten handbreadths in all area of four cubits. Hence it must either be spanned or pierced.');"><sup>35</sup></span> but here it is a case of one that cannot conveniently be used.<span class="x" onmousemove="('comment',' A wall, for instance, that rose sharply in a perpendicular direction. As its sides are of no use for walking purposes they may be disregarded and only the estimated thickness of the wall need be included in the measurements.');"><sup>36</sup></span> Rab Judah citing Samuel stated: This<span class="x" onmousemove="('comment',' That the method of piercing is admissible.');"><sup>37</sup></span> was learned only in the case where a plumb line<span class="x" onmousemove="('comment',' Suspended from the edge of the glen and reaching the bed.');"><sup>38</sup></span> does not descend in a straight line<span class="x" onmousemove="('comment',' Lit., 'corresponding to it'. This is defined infra 58b.');"><sup>39</sup></span>