THE THAMES TUNNEL. 143 



and turned so as to press against the brickwork, and used to propel each 

 division forward. 



The divisions of the shield were advanced separately and independently 

 of each other by the means before mentioned ; each division with boards 

 in front (known by the technical name of polling boards), supported and 

 kept in position by means of jack screws, which were lodged against the 

 front of the iron frame; these boards being in succession taken down, while 

 the earth in front of which was excavated, the first board being always 

 replaced before a second was removed, thus forming a constant firm 

 buttress. 



The interior is quite a fairy scene, and consists of two immense 

 avenues, brilliantly lighted with gas; these avenues are divided by a 

 'thick wall of brick-work, which is firmly set in cement ; the middle 

 wall is for greater security, while in progress, built quite solid, but for 

 convenience, light, and general effect, a succession of arches are opened 

 in that middle wall, so as to admit of frequent communications between 

 the two carriage ways. 



In November, 1839, the Tunnel was completed to the extent of 30 feet, 

 beyond low watermark, on the Middlesex side, and then progressed 

 at the weekly average rate of three feet ; the whole extent being 1,300 feet. 



To facilitate the access to the Tunnel, the carriage-way is by 

 circular descents, an d does not exceed , in any part the slope of Ludgate Hill , 

 or Waterloo Place, Pall Mall. 



From the great success attending the completion of this stupendous 

 undertaking, it is almost ungracious to notice former failures ; 

 but we do so only to express our admiration at the scientific 

 resources of that mind which has overcome all but insuperable obstacles. 

 The works were thrice interrupted, in 1826, by the breaking off of the 

 clay, leaving the shield exposed to the influx of land water for six weeks; 

 on the 18th May, 1827, and again in January, 1828, when the river 

 broke in and filled the Tunnel; this was quickly remedied by filling the 

 holes or chasms with strong bags of clay ; the structure, however, on 

 clearing the tunnel of the water, was found in a most satisfactory state. 



The works from that time were suspended for seven years, when they 

 were again resumed, and the workmen have continued their labours, to 

 the satisfactorily surmounting of all obstacles. As to the ultimate 

 pecuniary success of the speculation, that may be problematical; but 

 should it prove a loss to the Company, it is to be hoped Government 

 will make it a " National Affair," and take it into their own hands. 



