WEIGHT OF DIFFERENT PARTS. 27 



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. 



Similarly, if disk No. 2 is cut up as in the figure, the specific weight 

 of the different pieces 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 summerwood bands. 



Cutting up all disks in the same way, it will be found that the piece 

 a of the first disk is heavier than 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 their radial 

 surfaces and set up one on top of the other in their regular order for 

 sake of comparison, tbis decrease in weight will be seen to be accom- 

 panied 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 subse- 

 quent decrease could have been observed. 



In a thrifty young pine, then, the wood is 

 heavier from the center outward, and lighter FlG - "—orientation of wood 

 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 successive piece 

 from the center outward is lighter than its inner neighbor. 



Examining the pieces, this difference is not as readily explained by 

 the appearance of each piece as in the case of pine wood. Neverthe- 

 less, one conspicuous point appears at once, the pores, so very distinct 

 in oak, are very minute in the wood near the center and thus the wood 

 is far less porous. Studying different trees it is found that, in the pines, 

 wood with narrow rings is just as heavy as, and often heavier than 

 the wood with wider rings, but if the rings are unusually narrow in 

 any part of the disk the wood has a lighter color; that is, there is less 

 summer wood and therefore less weight. 



In oak, ash, or elm trees of thrifty growth, the rings fairly wide (not 

 less than one-twelfth inch), always form the heaviest wood, while any 



ditt.3 



ditc.Z 



dine J 



