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The cracks in walls will never be parallel unless the part of the wall that separates from the remainder does not slip down.
The stability of buildings is the result of the contrary law to the two former cases. That is to say that the walls must be all built up equally, and by degrees, to equal heights all round the building, and the whole thickness at once, whatever kind of walls they may be. And although a thin wall dries more quickly than a thick one it will not necessarily give way under the added weight day by day and thus, [16] although a thin wall dries more quickly than a thick one, it will not give way under the weight which the latter may acquire from day to day. Because if double the amount of it dries in one day, one of double the thickness will dry in two days or thereabouts; thus the small addition of weight will be balanced by the smaller difference of time [18].
The adversary says that a which projects, slips down.
And here the adversary says that r slips and not c.
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.
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.
78:400 : 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.