THE SEVERN TUNNEL. 



67 



did, spend an hour in tlie vain ondeavour to fix tliom, until 

 your handkerchief is wet through with mopping up your 

 tears, but you are never sure of accuracy. In addition to 

 this, thcA-o was a considerable jar in the bottom at every 

 stroke of the big pump, which shook the wires and kept 

 them in a nearly constant tremor. So tliis plan was aban- 

 doned and a now one adopted. A good ti-ansit instrument 

 was obtained for the purpose from Messrs. Trougliton & 

 Simms, with a four-inch hole in the bottom plate, through 

 which the telescope could be pointed vertically downwards, 

 and a largo block of stone was built solidly into the shaft 

 wall on top to carry the transit; the heavy end of the stone 

 was built into the wall, but a lighter end projected two feet 

 into the shaft. On this lighter end the ceuti'e lino of the 

 tunnel had been marked, and an eight-inch peep hole cut 

 through it. This formed the apparatus for the shaft top. 

 For the bottom a pianoforte wire, about two hundred and 

 fifty feet long, was ])rocnrod, and a couple of tine-threaded 

 screws, made each about six inches long, and mounted on a 

 bed plate which could bo firmly screwed down to a beam of 

 timber. Then a beam was strongly fixed across the back of 

 the shaft bottom furthest from tlie heading, which was then 

 only being driven towards the river, and another beam 

 across the heading within a foot or two of the full length of 

 the wire; the adjusting screws were fixed upon those beams 

 m their proper places, for the position of the centre-line was 

 known very nearly at the sliaft bottom, and pretty nearly at 

 the two hundred and fifty feet along the heading, which was 

 then perhaps two hundred yards in. The wire was then 

 carefully uncoiled off its reel, so as to leave no kinks, and 

 each end was passed simply over the thread of the screw at 

 <'ach end with a 28 lb: weight suspended from it. This 

 kept the wire clear of the heading floor all along. The 



