The Progress of Invention in the Nineteenth Century. by Edward W. Byrn

No. 3,226, of 1861. It consists of a vertical cylinder divided into compartments, its lower open end resting on the river bottom. Compressed air forced into the lower compartment forces the water back, while the men are at work, the intermediate chamber forming an air lock, by which entrance to, or egress from, the lower working chamber is obtained. The pneumatic caissons of Eads (patents Nos. 123,002, January 23, 1872, and 123,685, February 13, 1872) and Flad (patent No. 303,830, August 19, 1884) are modern applications of the same principle. The sinking of shafts through quicksand, by artificially freezing the same and then treating it as solid material, is an ingenious modern method shown in patents to Poetsch, No. 300,891, June 24, 1884; and Smith, No. 371,389, October 11, 1887. _Tunnels._--Less conspicuous than bridges, by virtue of their underground character, but none the less important, are these mole-like means of communication. Especially difficult of construction for the reason that the nature of the soil or rock is largely unknown, and for the reason also that the work may have to encounter faults in rocks, and springs or quicksands in the earth; nevertheless the demands of the railroads for shortening the distance of travel and economizing time have stimulated the engineer to expend millions of dollars in piercing the earth with these great underground passageways. _The Mont Cenis Tunnel_ was constructed to establish railway communication between France and Italy through the Alps. It was begun in 1857, and after having been in progress of construction for thirteen years, was opened for traffic in 1871. This tunnel was commenced by hand borings, being for the most part through solid rock, and its progress up to 1862 was so slow that it was estimated that thirty years would be required for its construction. Its earlier completion was due to the