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.
1. That which gets wet increases in proportion to the moisture it imbibes.
2. And a wet object shrinks, while drying, in proportion to the amount of moisture which evaporates from it.
[Footnote: The text of this passage is reproduced in facsimile on
Pl. CVI to the left. L. 36-40 are written inside the sketch No. 2.
L. 41-46 are partly written over the sketch No. 3 to which they
refer.]
773.