32 



TKOHNIOAL PROPfiBHES OF WOOD. 



be a very recent one. Logs affected with only a simple shake 

 usually lose nothing of their value as sawyer's timber, but a bad 

 star-shake renders the wood fit only for fuel. Nevertheless very 

 fine compound shakes are no great disadvantage in the case of 

 large beams. 



B. Radial-shakes. — Radial-shakes, contrary to heart-shakes, al- 

 ways begin at the circumference of the standing tree and extend 

 inwards. They are due to the outer concentric zones of growth 



Fig. 2. 



— b 



Radial Shake, 



a. An nld ime closed, b. A new one itiU open. 



V. A still more recent one. 



contracting so as to be no longer able to completely encircle the 

 inside solid cylinder of wood. Thus a crack or cracks occur. 

 The contraction may be due to sudden excessive cold, or to a very 

 hot sun after a chilly night, or to hot blasts of wind , or to forest fires ; 

 the more sudden the change of temperature the more effective it is, 

 as the difference of temperature between the outer and inner zones 

 is then greater. A radial-shake will always occur on the most ex- 

 posed side of the trunk. When the difference of temperature 

 which caused the shake has disappeared, the crack closes up, and, in 

 the absence of further accidents for a year or two, may be grown 

 over and completely concealed by the new concentric zones of 

 wood. But, on the other hand, the crack may re-open year after 

 year, in which case a continuous ridge formed by the thicker 

 growth of wood along the lips of the long wound (where of 

 course there is less pressure thiui elsewhore) will indicate the 



