Rock Drill.
It is by our system of using sharp curves that we avoid tunnels. It may be said, in general terms, that American engineers have shown more skill in avoiding the necessity of tunnels than could possibly be shown in constructing them. When we are obliged to use tunnels, or to make deep cuttings in rocks, our labors are greatly assisted by the use of power-drills worked by compressed air and by the use of high explosives, such as dynamite, giant powder, rend-rock, etc. Rocks can now be removed in less than half the time formerly required, when ordinary blasting-powder was used in hand-drilled holes.[3]
A Construction and Boarding Train.
III.
From data furnished by Mr. D. J. Whittemore, chief engineer of the Chicago, Milwaukee, and St. Paul system (which had a total length of 5,688 miles on January 1, 1888), the length of open bridges on these lines was 11591/100 miles, and of culverts covered over with embankment, 392/10 miles. "Everything," says Mr. Whittemore, "not covered with earth, except cattle guards, be the span 10 or 400 feet, is called a bridge. Everything covered with earth is called a culvert. Wherever we are far removed from suitable quarries, we build a wooden culvert in preference to a pile bridge, if we can get six inches of filling over it. These culverts are built of roughly squared logs, and are large enough to draw an iron pipe through them of sufficient diameter to take care of the water. We do this because we believe that we lessen the liability to accident, and that the culvert can be maintained after decay has begun, much longer than a piled bridge with stringers to carry the track. Had we good quarries along our line, stone would be cheaper. Many thousands of dollars have been spent by this company in building masonry that after twenty to twenty-five years shows such signs of disintegration that we confine masonry work now only to stone that we can procure from certain quarries known to be good."
Bergen Tunnels, Hoboken, N. J.
Mr. Whittemore is an engineer of great experience, skill, and judgment, and there is food for much reflection in these words of his: First—that it is better to use temporary wooden structures, to be afterward renewed in good stone, rather than to build of the stone of the locality, unless first-class. Second—that a structure covered with earth is much safer than an open bridge; which, if short and apparently insignificant, may be, through neglect, a most serious point of danger, as was shown in the dreadful accident of 1887 on the Toledo, Peoria, and Western road in Illinois, where one hundred and fifty persons were killed and wounded, and by the equally avoidable accident on the Florida and Savannah line, in March, 1888. Had these little trestles been changed to culverts covered with earth, many valuable lives would not have been lost.
