132 Dr. W. J. Bussell. On the Adim of Wood [May 28, 



f in the wood but it is remarkable that 



* en found to behave in the same way as the Scotch fii . 



With the spruces the action on the plate is not so definite and well 

 marked ; the white wood is always active, but m some cases the dark 

 rin's ar'e also active, and the pictures are not so sharp as with the 

 firs Larch wood gives a very interesting result, lor the picture is 



FIG. 1. 



the reverse of that of the Scotch fir, that is, the dark rings in the 

 wood are the active rings and the light rings are inactive. 



With regard to woods other than conifers, oak and beech are both 

 active and give very good pictures, so also does acacia (Eobinia), 

 Spanish chestnut, and sycamore ; on the other hand, ash, elm, horse 

 chestnut, plane are comparatively but slightly active. In the full 

 paper lists of woods are arranged according to their activity. 



Many foreign woods are very active, but as the annual rings are 

 often not well developed, the pictures they give are of a somewhat 

 different character. The African black wood, rose wood, cocobola, 

 and many others are very active. Several of the foreign woods have 

 a ring of white wood which is quite inactive. 



Knots in a wood generally, but not always, give a good picture. 



