kinds.

When kiln-dried, the misleading moisture factor of weight is uniformly
reduced, and a fair comparison possible. For the sake of convenience
in comparison, the weight of wood is expressed either as the weight
per cubic foot, or, what is still more convenient, as specific weight
or density. If an old long-leaf pine is cut up (as shown in Fig. 21)
the wood of disk No. 1 is heavier than that of disk No. 2, the latter
heavier than that of disk No. 3, and the wood of the top disk is found
to be only about three fourths as heavy as that of disk No. 1.
Similiarly, if disk No. 2 is cut up, as in the figure, the specific
weight of the different parts is:

_a_, about 0.52
_b_, about 0.64
_c_, about 0.67
_d_, _e_, _f_, about 0.65

showing that in this disk at least the wood formed during the many
years' growth, represented in piece _a_, is much lighter than that of
former years. It also shows that the best wood is the middle part,
with its large proportion of dark summer bands.

[Illustration: Fig. 21. Orientation of Wood Samples.]

Cutting up all disks in the same way, it will be found that the piece
_a_ of the first disk is heavier than the piece _a_ of the fifth, and
that piece _c_ of the first disk excels the piece _c_ of all the other
disks. This shows that the wood grown during the same number of years
is lighter in the upper parts of the stem; and if the disks are
smoothed on the radial surfaces and set up one on top of the other in
their regular order, for the sake of comparison, this decrease in
weight will be seen to be accompanied by a decrease in the amount of
summer-wood. The color effect of the upper disks is conspicuously
lighter. If our old pine had been cut one hundred and fifty years ago,
before the outer, lighter wood was laid on, it is evident that the
weight of the wood of any one disk would have been found to increase
from the center outward, and no subsequent decrease could have been
observed.

In a thrifty young pine, then, the wood is heavier from the center
outward, and lighter from below upward; only the wood laid on in old
age falls in weight below the average. The number of brownish bands of
summer-wood are a direct indication of these differences. If an old
oak is cut up in the same manner, the butt cut is also found heaviest
and the top lightest, but, unlike the disk of pine, the disk of oak
has its firmest wood at the center, and each