33O COMPOSITE ORGANS. CHAP. II. 



former account for it by telling us it is because 

 the north side is sheltered from the sun ; and the 

 latter by telling us it is because the south side is 

 sheltered from the cold ; and thus from the opera- 

 tion of contrary causes alleging the same effect, 

 which has been also thought to be sufficiently 

 striking and uniform to serve as a sort of compass, 

 by which the bewildered traveller might safely steer 

 his course, even in the recesses of the most ex- 

 tensive forest. But if this were even the fact, it 

 would certainly prove to be one of the most in- 

 commodious compasses that was ever invented. 

 For if the traveller must undergo the labour of 

 cutting down a tree every time he may want to 

 know his bearings, it is to be believed he will soon 

 become tired of his instrument of observation. 



But Duhamel has exposed the futility of this 

 notion, by showing that the excess is sometimes 

 on the one side of the axis, and sometimes on the 

 other, according to the accidental situation of the 

 great roots and branches ; a thick root or branch 

 producing a proportionably thick layer of wood 

 on the side of the stem from which it issues. The 

 layers are indeed sometimes more in number on 

 the one side than on the other, as well as thicker. 

 But this is the exception, and not the rule. They 

 are thickest however on the side on which they are 

 fewest, though not of the same thickness through- 

 out. Duhamel after counting twenty layers on the 

 one side of the transverse section of the trunk of 





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