120 
WHITE PINE. 
evidence of persons of the greatest experience in ship- 
building.” ( M l CullocK > s Commer. Diet., article Timber 
Trade.) There is no doubt a good deal of truth and some 
prejudice in these statements, particularly as regards the 
durability of White Pine timber, as any one will acknow- 
ledge on inspecting the present condition of the Schuylkill 
bridge at Philadelphia, which, after 37 years have elapsed 
since its erection, is apparently as sound as ever. 
From S. W. Roberts, Esq., civil engineer, we learn that 
the superstructure of the large wooden bridges, so nume- 
rous in Pennsylvania, is principally constructed of White 
Pine. The lattice bridges are built of thick White Pine 
planks, for which use this timber is well adapted on ac- 
count of its lightness, freedom from warping, and the ease 
with which it is worked. The Yellow Pine being harder 
is better for the posts of the bridges, because it undergoes 
less compression. These bridges are generally roofed and 
weather-boarded, but not ceiled, so that the frame timber 
is protected from the weather but exposed to the air. In 
such situations good White and Yellow Pine posts and 
beams of moderate size, season without injury from dry- 
rot, and last so long, that Mr. Roberts has no experimental 
knowledge of their comparative durability, but he supposes 
that the Yellow Pine will be the most durable, as it con- 
tains the most resin. 
Mr. Roberts remarks, that the thin weatherboarding of 
White Pine on the sides of frame houses, although thus 
exposed, remains sound for a generation, even without 
paint. 
“One of the greatest wooden bridges probably in the 
world, is the aqueduct over the Alleghany river at Pitts- 
burg, through which the state canal passes. It has seven 
spans of one hundred and sixty feet each, with a water- 
