THE STRENGTH OF TIMBER. 



585 



nical 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 e 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 me- 

 dullary rays are thus brought closer by the collapsing of the vertical 

 fibres. 



Fig. 1. 



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 sea- 

 soning 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 



Fig. 2. 



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 



