THE SEVERN TUNNEL. 59 



liaving a heavy leaden weight at the bottom end. This 

 reel was controlled by a light hand-brake, by which the 

 wire was kept siiffioieiitly taut as tho lead went down, and 

 by which the reel was stopped the instant it struck the 

 bottom. Tho reel also worked an index round a dial plate, 

 which was divided into feet and tenths ; so that the depth 

 could be read off in a moment with precision. At the end 

 of tho reel there was a handle, by which tho wire could bo 

 reeled up again rapidly for another sounding. 



Tho lirst engineer at the bow stood over tho sounding 

 machine with a sextant in his hand, got the boat into lino 

 with tho two poles, and called oat "Now!" taking at the 

 same time the angle to the lateral pole. The second ongi- 

 iioer, with the sounding machine, immediately let down the 

 2)lamniet. The third engineer, with the tiller in one hand 

 and his watch in the other, called the exact time ; and the 

 fourth noted tlie figures in a book ruled for tho purpose— 

 tlie angle first, the time second, and the depth third — as 

 they were called out. 



At tlie same time a man on sliore was noting tho heights 

 of the water at every minute from a gauge that had been 

 fixed there for the purpose. The soundings were afterwards 

 reduced to the correct water levels, and the height of each 

 sounding above Severn Tunnel datum entoi'od in its proper 

 column. 



By these moans really correct sections of the Shoots' 

 bottom were obtained. Tho soundings wore ta,ken as close 

 together as possible ; and when two soundings happened to 

 be taken on the same spot, they always tallied. 



Wlicn all tho linos of soundings had been taken, and tho 

 results plotted, they were found to differ so little either 

 in the form of the bottom or in the depth of the water, that 

 one point of crossing was practically as good as another. 



