108 Notes on the Properties of Wood. 
imperfect, it is owing to either the loss or the freezing of 
the branches. Then again, it may have been caused by 
insects and larger animals who live upon and in trees, or 
by dryness. 
The unequal width of the rings is the main feature by 
which we judge of the physical condition of the wood, and 
therefore we will examine this point closely. 
The healthy life of a tree requires, as a necessity, a 
certain modicum of light and a constant supply of fresh 
air, besides the nourishment which it absorbs from the 
soil, through the media of its roots. A tree transferred to 
a more suitable climate or richer soil, will be found to im- 
prove its condition; but should any element be found 
wanting, that tree will not improve, or perhaps it may in- 
crease in size, losing, on the other hand, its specific weight. 
The Fir, which grows on very dry marl, forms narrow 
yearly rings; if on rich and damp marl, they are wide; but 
when on wet soil they are again smaller. The common 
Fir, on moor soil, has smaller yearly rings than if on dry 
sand or marl. It is evident from this, that too dry or too 
wet a soil is not suitable for the development of this tree. 
A white fir-tree, twenty-five years old, situated in a tolera- 
bly suitable ground, may have a diameter of three inches 
or so, whilst another on dry ground will be but one inch 
thick. If we submit a cross-section of each under the 
microscope, the former will appear like a net with large 
pores, whilst the second looks almost like one solid mass. 
The greatest amount of attention should be given to 
this fact in the selection of masts and spars for ship-build- 
ing. The usual width of the rings in the Fir when young is 
2°4 mil. with a slight decrease towards the bark. In the 
Swedish and Russian firs the smallest rings are found, 
which is ascribable to the shortness of the summer in those 
climates, but still the same result obtains in more southerly 
latitudes. 
The Leafwoods, with large pores, analogous, but opposite 
to those of the Pines, with them, although the rings become 
smaller, the quantity or bulk of the porous springwood 
does not decrease in the same ratio. A cubic inch, there- 
fore, contains more mass, the less we find pores in the same, 
or in other words, the broader the yearly rings so much the 
greater will be the mass of the wood. The reason for this 
is, that the pores are considerably smaller on trees with — 
broader yearly rings, and are, at the same time, less — 
numerous. The outer rings of trees are often found as 
