Figure 19. — The successive stages in the enlargement of 

 a mid- 19th-century railroad tunnel, using the Austrian 

 system of timbering. MHT model. 



Figure 20. M. I. Brunel's Thames Tunnel, 1825-1843,1116 first driven beneath a body of water. 

 Mil T model — y 4 " scale. (Smithsonian photo 49260-F.) 



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II I I I I IN 240: CONTRIBUTIONS FROM THE MUSEUM OF HISTORY AND TECHNOLOGY 



