220 Tl'NNKUNc; 



700 tons on the whole shield (Fig- 118). These jacks were 

 controlled by two block-valves, one placed on each side of 

 the shield. Each of these block-valves consisted of six inde- 

 pendent valves all in one compact casting, each of which had a 

 pressure and exhaust stem. Half-inch XX pipe was used for 

 connecting each jack with its valve, and 1-in. hydraulic pipe 

 was used for the pressure main, which was connected with the 

 shield block-valves by three swivel-joint connections. To fur- 

 nish the pressure, a very compact little pump, designed by 

 Watson & Stillman, of New York, was used without an accu- 

 mulator, the pressure being very nicely governed by a steam- 

 regulating valve. 



On Sept. 22 work was resumed on the New York side, 

 with a small force of men working days only, to excavate in 

 the rock an enlarged chamber about 15 ft. back from the face, 

 in which to erect the shield. This chamber was made circular, 

 tibout 15 ft. in diameter and 10 ft. long. Back from this, the 

 rock was taken out in a circular form of about 11 ft. diameter, 

 for some 14 ft., or enough for about 10 rings of the cast-iron 

 segments which were here erected in the rock, the spaces be 

 tween being thoroughly grouted with Portland cement. These 

 rings were thus made solid in the rock to withstand the thrust 

 of the shield- jacks upon the lining. The blasting necessary in 

 this work was made as light as possible ; but it was not without 

 its effect upon the soft material in the heading, a considerable 

 quantity of the black mud being washed through the bulkhead, 

 while the braces showed signs of a heavy strain from the 

 squeezing of the material. The shield arrived at the works on 

 Nov. 10, and the work of erection was immediately begun. 

 The sections were lowered down the shaft and taken through 

 the air-lock to the shield-chamber. On Nov. 17 the shield was 

 all assembled, and riveting the tail-end sections was commenced. 

 For heating the rivets in the air-chamber a forge was used, 

 with a hood to which was connected at the top a 2-in. pipe with 

 a valve which extended through the air-lock bulkhead. By 



