The adversary says that _a_ which projects, slips down.
And here the adversary says that _r_ slips and not _c_.
HOW TO PROGNOSTICATE THE CAUSES OF CRACKS IN ANY SORT OF WALL.
The part of the wall which does not slip is that in which the obliquity projects and overhangs the portion which has parted from it and slipped down.
ON THE SITUATION OF FOUNDATIONS AND IN WHAT PLACES THEY ARE A CAUSE OF RUIN.
When the crevice in the wall is wider at the top than at the bottom, it is a manifest sign, that the cause of the fissure in the wall is remote from the perpendicular line through the crevice.
[Footnote: Lines 1-5 refer to Pl. CV, No. 2. Line 9 _alle due anteciedete_, see on the same page.
Lines 16-18. The translation of this is doubtful, and the meaning in any case very obscure.
Lines 19-23 are on the right hand margin close to the two sketches on Pl. CII, No. 3.]
OF CRACKS IN WALLS, WHICH ARE WIDE AT THE BOTTOM AND NARROW AT THE TOP AND OF THEIR CAUSES.
That wall which does not dry uniformly in an equal time, always cracks.
A wall though of equal thickness will not dry with equal quickness if it is not everywhere in contact with the same medium. Thus, if one side of a wall were in contact with a damp slope and the other were in contact with the air, then this latter side would remain of the same size as before; that side which dries in the air will shrink or diminish and the side which is kept damp will not dry. And the dry portion will break away readily from the damp portion because the damp part not shrinking in the same proportion does not cohere and follow the movement of the part which dries continuously.
OF ARCHED CRACKS, WIDE AT THE TOP, AND NARROW BELOW.
Arched cracks, wide at the top and narrow below are found in walled-up doors, which shrink more in their height than in their breadth, and in proportion as their height is greater than their width, and as the joints of the mortar are more numerous in the height than in the width.
The crack diminishes less in _r o_ than in _m n_, in proportion as there is less material between _r_ and _o_ than between _n_ and _m_.
Any crack made in a concave wall is wide below and narrow at the top; and this originates, as is here shown at _b c d_, in the side figure.