SI ll.MAUlNi: TrNNKI.INC 'J43 



the ship-worm, on which it is alleged to have been modeled, was 

 remarkably rl<r. 



In the same patent in whirh Sir Isamhard secured protection 

 for liis mechanical silkworm he elaimed equal rights of inven- 

 tion for another shield, which is of far greater importance in 

 being the prototype of the shield actually en ployed by him in 

 constructing the first Thames tunnel. This alternative inven- 

 tion, if it may be so termed, consisted of a group of separate 

 cells which could be advanced one or more at a time or all 

 together. The sides of these cells were to be provided with 

 friction rollers to enable them to slide easily upon each other; 

 and it was also specified that the preferable motive power for 

 advancing the cells was hydraulic jacks. To sumntari/e briclly, 

 therefore, the two inventions of Brunei comprehended the pro- 

 tecting cylinder or shield, the closure of the face of the exca- 

 vation, the cellular division, the hydraulic-jack propelling po\\er, 

 and cylindrical iron lining, which are the essential characteris- 

 tics of the modern shield system of tunneling. The next step 

 required was the actual proof of the practicability of Brunei's 

 inventions, and this soon came. 



Those who have read the history of the first Thames tunnel 

 will recall the early unsuccessful attempts at construction which 

 had discouraged English engineers. Five years after Brunei's 

 patent was secured a company was formed to undertake the 

 task attain, the plan l>eing to use the shield system, under the 

 >nal direction of its inventor as chief engineer. For this 

 work Brunei selected the cellular shield mentioned as an alter- 

 native construction in his original patent. He also chose to 

 make this shield rectangular in form. This choice is commonly 

 accounted for by the fact that the strata to l>e penetrated by the 

 tunnel were practically hori/oiital. and that it was assumed by 

 the engineer that a rectangular shield would for some reason 

 ~t the pressures which would !>e developed. Whatever 

 the reason may have In-cn for the choice, the fact remains that 

 a rectangular shield was adopted. The tunnel as designed con- 



