4 68 



THE POPULAR SCIENCE MONTHLY. 



that two single-track tunnels would be cheaper, and one of them 

 would sooner be available for traffic. Experience has proved that 

 a second tunnel will not be required for a long time. The largest 

 number of freight cars passed through in twenty-four hours 



FIG. 4. SECTION OF THE TUNNEL AND RIVER-BED. 



during the two years the tunnel has been in use was one thou- 

 sand and fifteen, while twenty-five hundred could be handled if 

 occasion required. The average number is seven hundred in 



