G54 



HISTORY OF THE SEA. 



part supported three shafts — a middle and two lateral ones 

 All three shafts arose above the water of the river. The mid 

 die shaft communicated with the open air, and the water rose 

 in it to the level of the river. In this a dredging machine, 

 driven by a steam-engine above, worked at the bottom of the 

 river. The other two shafts were closed at the top. The work 

 men entering above the stream, closed their means of ingress, 

 air tight, and then air was forced in until the water was forced 

 down, and out below, leaving the shafts free. The workmen 

 then descended and filled the buckets of the dredging machine. 

 When they wanted to ascend, they mounted to the upper part 

 of the shafts ; the air was let off, the water mounted in the 

 shafts and they stepped into the open air. 



The abutments of the bridge over the East River, which is 

 to connect New York and Brooklyn by a suspension bridge, 

 with a span high enough to not interfere with the navigation 

 of the river, were built with a somewhat similar device. The 

 towers upon each side of the river had to be so high that a 

 very deep foundation, going down to the original rock, had to 

 be laid, and the workmen engaged in building it worked in a 

 submarine apartment, supplied with air forced down by a steam 

 engine. 



The submarine hydrostat, as it is called, is one of the most 

 ingenious and recent applications of the diving-bell principle. 

 Thirty men may work in it at once, for a number of hours, 

 without any inconvenience; while beside this it enables them 

 at will, to float or sink. 



Externally, as will be seen £rom the upper structure in the 

 cut, the machine is a rectangular box, surmounted with an 

 other smaller one, entirely closed except at the bottom. The 

 interior of the hydrostat consists of three principal compart- 

 ments ; the lower figure in the cut represents these in section. 

 The lower one, or hold, is open below, and communicates by a 

 shaft with the up^er compartment. Between the upper and 



