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THE POPULAR SCIENCE MONTHLY. 



will be pulled round or bent convex, while the outside will be the re- 

 verse, or hollow, and the plank will be considerably narrower through- 

 out its entire length, more especially on the surface of the hollow side. 

 Selecting the next two planks, they will be found to have lost none of 

 their thickness at the centre, and very little of their thickness at the 

 edges, but very much of their breadth as planks, and will be curved 

 round on the heart-side and made hollow on the outside. Supposing 

 some of these planks to be cut up into square prisms when in the 

 green state, the shape that these prisms will assume after a period of 

 seasoning will entirely depend on the part of the tree to which they 

 belong, the greatest alteration would be perpendicular to the medul- 



Fig. 8. 



Fig. 4. 



lary rays. Thus, if the square was originally near the outside, as seen 

 in Fig. 3, then the effect will be as shown in Fig. 4, namely, contrac- 

 tion in the direction from a to b. After a year or two the square end 

 of the prism will become rhomboidal, the distance between c and d 

 being nearly the same as at first, but the other two edges brought 

 closer together by the amount of their contraction. By understand- 

 ing this natural law, it is comparatively easy to predict the future be- 



Fig. 5. 



Fig. 6. 



havior of a board or plank by carefully examining the end-wood, in 

 order to ascertain the part of the log from which it has been cut, as 

 the angle of the ring-growths and the medullary rays will show this, 

 as in Figs. 5 and 6. If a plank has the appearance of the former, it 

 must have been cut from the outside, and for many years it will grad- 



