150 



THE BOOK OF NATURE STUDY 



oak, elm, ash, beech, alder, and sycamore are hard woods; the 

 larch is considered a medium wood as regards hardness. The 

 timber of the British oak is unequalled by that of any other 

 species for the combination of size, strength, and durability ; 

 it stands greater strain than any other species, and is very much 

 used for the framework of railway waggons. Some few years ago 

 the experiment was tried of building six railway waggons of 

 British oak and six of the best foreign oak ; all the waggons were 

 used for similar purposes. By the time the six British ones came 

 in for repair, the others were worn out. For general wheelwright 



work, where there is great 

 strain, as in the spokes of 

 wheels, and much exposure 

 to weather, there is nothing 

 equal to our oak. From a 

 saw-mill a section of oak, 

 larch, and beech may be ob- 

 tained and compared with 

 each other ; the section 

 should be three or four inches 

 thick, and, if varnished, it 

 keeps cleaner, and may be 

 used year after year for 

 lessons. The most noticeable 

 character about the sections 

 is the arrangement of the wood in rings. This is due to the 

 fact that trees do not form wood of the same quality, or texture, 

 throughout the year. The wood formed at the end of the 

 summer period of growth is very different from that* produced 

 in the spring, when the winter's rest is over. The late-formed 

 wood is closer than that of spring, and as the spring growth 

 of one year immediately follows on to the summer or autumn 

 growth of the preceding year, distinct rings are formed, each ring 

 representing a whole year's growth ; the age of a tree, when felled, 

 is thus known. The average age of an oak is nine hundred years, 

 and it may even reach fifteen hundred ; yews are said to attain 

 some three thousand years. 



Some trees deteriorate if a wood consists but of the one 



L-.S. 



-... 



FIG. 42. Branch of Larch (transverse section). 

 d, Heart wood ; s, sap wood ; e, bark. 



