PREFACE. i r 



polishing test is based upon the time and trouble expended in 

 producing a passable finish, as any wood can be made to take a 

 high polish if desired. A soft, spongy wood will absorb coat 

 after coat of polish, and a hard wood, which may leave the cutting- 

 edge of a tool with a natural polish, may yet be very trouble- 

 some on account of the amount of filling required by the open 

 pores in order to bring the surface level. Spirit polish often 

 modifies the colour of a wood profoundly ; Purpleheart becomes an 

 uninteresting brown colour with this polish. 



The superficial comparison of the radial and tangential sec- 

 tions of wood ("quartered" wood and " plankwise ") may be 

 very misleading. No two planks can be exactly alike except by 

 accident. In this series the increase in the size of the pores 

 from the pith outwards is very marked, and in some cases th 

 difference is so great that a piece of wood taken from the same 

 block near the bark may be so much coarser in the grain compared 

 with a piece from the neighbourhood of the pith, that they may 

 appear sufficiently dissimilar to seem different species. 



The weights per cubic foot have been ascertained by measuring 

 and weighing square, air-dried blocks. In no case has a nearer 

 weight than Ib. per cubic foot been given, as different parts of 

 the same plank will differ as much. The practice of giving the 

 specific gravity of woods to three and four places of decimals is a 

 preposterous proceeding; besides which an average figuie is mis- 

 leading when the variation of the specific gravity in a species is 

 great. The average weight per cubic foot of the Scots Fir or 

 Pine is 36 Ibs., but one may meet with specimens as low as 20 Iba., 

 or as high as 52 Ibs. 



Where the weight per cubic foot has been ascertained from the 

 specimens in this collection only, but one figure can be given. 

 In other cases, where records exist, the highest and lowest are 

 quoted in order to indicate the variation that may be expected. 

 Further records are greatly needed in connection with the le*s 

 known species. 



The colour and other qualities may vary in like manner to the 

 specific gravity, so that different statements by various author* 

 are not necessarily contradictions. The wood of a -slowly-grown 

 tree will be heavier, tougher, denser, closer in the grain, darker 

 and richer in colour, than one making wood rapidly; on the 

 contrary, the latter will display the characteristic structure of the 

 species more clearly. When examination with the lens is resorted 

 to, the best-developed zones must be sought for. 



