32 



TIMBER AND TIMBER TREES. 



CHAP.] 



well aware of this, that he will study to leave, if possible, 

 in any work of construction, the outer side only exposed. 

 It is, therefore, necessary in every case to look for the 

 pith or centre of the stem, or — if that has been removed 

 by the conversion of the tree — for the innermost, or 



oldest layer of heart-wood, in the plank or board, as that 

 will be the inside of it. If this precaution is disregarded, 

 the innermost or earlier layers of wood lift and shell out, 

 after exposure for a time, In shreds and strips^ the 

 cohesion of the successive layers of wood having been 

 destroyed by the action of the atmosphere. Fig. i 



shows the plank properly fixed, with the inner or earlier 

 layers of wood against the beam, in which position they 

 do not so readily separate. Fig. 2 shows the plank im- 

 properly fixed, with the outer, or younger layers of wood 

 against the beam, in which position the earlier layers are 

 very liable to lift, or shell out, destroying the evenness 



