OF THE WOOD. 25 



year, the hard external part being caused by the cold 

 of winter ; consequently, that the exact age of a sound 

 tree when felled may be known by counting these 

 rings. It has even been asserted that the date of pe- 

 culiarly severe winters may be found in the harder 

 more condensed rings formed at those periods ; and 

 moreover, that the north side of a tree may always be 

 known by the narrowness and density of the rings on 

 that side. All this is controverted by Mirbel, chiefly 

 on the authority of Du Hamel, who nevertheless 

 scarcely says enough to invalidate the ancient opinion 

 on the whole. It is very true that there may be occa- 

 sional interruptions in the formation of the wood, from 

 cold or lickle seasons, and that in some trees the thin 

 intermediate layers, hardly discernible in general, which 

 unite to form the principal or annual ones, may, from 

 such fluctuation of seasons, become more distinct than 

 is natural to them. Such intermediate layers are even 

 found more numerous in some trees of the same species 

 and age than in others. But as there is always a most 

 material diflerence between summer and winter, so I 

 believe will there always be a clear distinction between 

 the annual rings of such trees as show them at all. 

 Trees of hot countries indeed, as Mahogany, and ever- 

 greens in general, have them but indistinctly marked ; 

 yet even in these they are to be seen. With regard to 

 their greater compactness on the north side of a tree, 

 Du Hamel justly explodes this idea. In fact, there is 

 most wood formed, and consequently these circles are 



