All About Inventions and Discoveries
The Romance of modern scientific and mechanical Achievements

 io2 All About Inventions clay and sand for a distance of 3| miles, from Stock- well to the Monument. It was opened in 1890, and attracted world-wide attention, because each road —the up and the down respectively—was laid in its own circular tunnel, interconnection being provided at certain stations. The tunnels were driven by means of the Greathead shield at depths varying from 50 to 80 feet, the excavators working upon the face in a compressed atmosphere. By this system of con- struction it was rendered possible to bore beneath the River Thames, the pressure within the shield being adequate to keep back the water and treacher- ous river-bed. The continuous burrow thus formed was lined with segments of iron bolted together, the internal diameter of the tunnel being 10 feet 2 inches. Owing to each train being confined to its particular tunnel, greatest safety was assured, the trains working in the manner of shuttles. The initial experiment having proved successful, other and more ambitious railways of a similar char- acter were taken in hand, with the result that the metropolis is now honeycombed with tube railways. By this means it has been possible to establish cheap and rapid communication between the City and suburbs which formerly were somewhat far apart, if not in miles, at least in travelling time. The con- venience of the public was further improved by the provision of interchanging facilities at various points, the outcome being that it is possible to travel from one part of the metropolis to another by tube. Similar systems were subsequently laid down in other cities, such as New York, Paris, and Buda-Pesth ; but in their construction the Greathead shield was not