584 THE POPULAR SCIENCE MONTHLY. 



and allowed to season or dry in a gradual manner, it is found to be the 

 most durable. In the arts, however, artificial drying is often resorted 

 to, as in the case of gun-stocks. These are put into a desiccating 

 chamber, where a current of air at 90 or 100 is passed over them, at 

 such a rate as to change the whole volume of air in the chamber every 

 three minutes, and it is found that a year of seasoning may thus be 

 saved. The walnut-wood is as good, after this process, as if the sea- 

 soning had been accomjdished by time and exposure, and works 

 more smoothly under the cutting instruments of the stock-machinerv. 



Wood will always warp after a fresh surface has been exposed, 

 and will likewise change its form by the presence of any moisture, 

 either from that contained in the atmosphere or from wetting the sur- 

 face. The effect of moisture on dry wood is to cause the tubular 

 fibres to swell ; hence it is that, if a plank or board is wetted upon one 

 side, the fibres there will be distended, and the plank, in consequence, 

 must bend. 



The natural law that governs the shrinking or contraction of tim- 

 ber is most important to practical men, but it is too often overlooked. 



The amount of the shrinkage of timber in length, when seasoning, 

 is so inconsiderable that it may in practice be disregarded. But the 

 shrinkage in transverse directions is much greater, and presents some 

 peculiarities which can only be explained by examining the structure 

 of the wood, as resulting from its mode of growth. An examination 

 of the end section of any exogenous tree, such as the beech or oak, 

 will show the general arrangement of its structure. It consists of a 

 mass of longitudinal fibrous tubes, arranged in irregular circles, which 

 are bound together by means of radial plates or rays, which have been 

 variously named : they are the " silver grain " of the carpenter, or the 

 " medullary rays " of the botanist, and are in reality the same in their 

 nature as the pith. The radial direction of these plates or rays, and 

 the longitudinal disposition of the woody fibre, must be considered 

 in order to understand the action of seasoning. For the lateral con- 

 traction or collapsing of the longitudinal fibrous or tubular part of the 

 structure cannot take place without first tearing the medullary rays, 

 hence the shrinking of the woody bundles finds relief by splitting the 

 timber in radial lines from the centre parallel with the medullary 

 rays, thereby enabling the tree to maintain its full diameter. If the 

 entire mass of tubular fibre composing the tree were to contract bodily, 

 then the medullary rays would, of necessity, have to be crushed in the 

 radial direction to enable it to take place, and the timber would thus 

 be as much injured in proportion as would be the case in crushing the 

 wood in a longitudinal direction. 



If an oak or beech tree is cut into four quarters, by passing the 

 saw twice through the centre at right angles, before the splitting and 

 contracting have commenced, the lines a c and b c in Fig. 1 would be 

 of the same length, and at right angles to each other, or, in the tech- 



