APPENDIX. 



NOTE TO FIG. 28. 



In the original pen drawing of an end view of one- 

 quarter of a log there were faintly shown concentric arcs to 

 represent the layers of growth . These did not " take " in 

 the photo-engraving. With a pencil and the common 

 attachment for drawing arcs these lines may be restored by 

 the pupil. But it would be a good plan to have a pupil 

 draw on the board a similar figure representing, natural size, 

 a log six feet in diameter. The boards one inch thick 

 should be separated by lines a quarter of an inch wide, 

 representing the saw-kerf, or that part of the log cut into 

 sawdust. Fine concentric lines a quarter of an inch apart 

 would represent the growths well enough. Lines narrower 

 than those separating the boards should be drawn at right 

 angles to them, four or five inches apart, to mark the saw- 

 kerfs of the saw used in " ripping " the boards into flooring; 

 In practise, however, the log is usually not first sawn into 

 wide boards, and these ripped; but that makes no difference 

 with our problem, which is to understand the relation be- 

 tween surfaces of boards and the growth-layers. With the 

 diagram and two pieces of real boards, representing the 

 extremes shown at a and ^, in Fig. 28, many practical 

 questions relating to lumber can be decided, and there is no 

 better educational work. Three or four exercises may well 

 be devoted to it. Fine lines radiating from the center would 



