i6 TIMBER AND TIMBER TREES. 



the physicist will surely have something to tell us about 

 our piece of wood. 



In the first place he will classify it among porous 

 bodies, and his attempts to investigate its properties from 

 his own points of view will help us to throw some light 

 on several points of interest. 



The physicist will also, no doubt, investigate the 

 specific gravity, the swelling and absorptive properties, 

 and the capillary phenomena exhibited by the piece of 

 wood, as well as its capacity for conducting sound, heat, 

 and electricity. 



First as to the specific gravity. This is a much less 

 simple matter than is immediately apparent at first sight. 

 The question arises, are we to regard the specific gravity 

 as ascertained by comparing the weight of a given 

 volume of our piece of wood — which we have seen 

 contains considerable quantities of water and air — 

 forthwith, and in the fresh state ; or are we to first dry 

 the wood, by driving off all the water, at i io° C. or so ; 

 or should we adopt some other method ? 



Obviously, no trustworthy results can be got by 

 the first method ; for the quantities of air and water in 

 a piece of fresh wood not only vary according to the 

 time of year, the part of the stem it is taken from, etc., 

 etc., but it is almost impossible to measure accurately a 

 body which is changing its volume so rapidly as a piece 

 of fresh wood does when once exposed to the air. 



The second plan would be to thoroughly dry a 

 large piece of the wood, and then cut a portion which 

 could be measured, and compare its weight with that of 

 an equal volume of water. But it is obvious that here, 

 again, what we really get is the specific gravity of the 

 wood plus imprisoned air, for the atmosphere drives air 

 in to replace the water expelled on heating; and the 



