Page:Popular Science Monthly Volume 2.djvu/605

Rh language of the workshop, they would be square; but, after being stored in a dry place, say for a year, a great change will be found to have taken place, both in the form and in some of the dimensions. The lines a c and b c will still be of the same length as before, but from a to b the wood will have contracted very considerably, and the two lines a c and b c will not be at right angles to each other, the angle being diminished by the portion shown in black in Fig. 1. The medullary rays are thus brought closer by the collapsing of the vertical fibres.



But, supposing that six parallel saw-cuts are passed through the tree, so as to form it into seven planks, what will be the behavior of the several planks? Consider the centre plank first. After due seasoning and contracting, it will be found that the middle of the board still retains the original thickness, from the resistance of the medullary rays, while the thickness will be gradually reduced toward the edges for want of support, and the entire breadth of the plank will be the



same as it was at first for the foregoing reasons, and as shown in Fig. 2. Then, taking the planks at each edge of the centre, by the same law their change and behavior will be quite different: they will still retain their original thickness at the centre, but will be a little reduced on each edge throughout, but the side next to the heart of the tree