SUB-MARINK VESSEL. 305 



mltted a fufficient quantity, he defcended very gradually ; if 

 he admitted too much, he ejecfled as much as was ncceffary 

 to obtain an equilibrium, by the two brafs forcing pumps, 

 which were placed at each hand. Whenever the veflel 

 leaked, or he would afcend to the furface, he alfo made ufe 

 of thefe forcing pumps. When the fkilful operator had ob- 

 tained an equilibrium, he could row upward, or down- 

 ward, or continue at any particular depth, with an oar, 

 placed near the top of the veflel, formed upon the principle 

 of the fcrew, the axis of the oar entering the vefl^el ; by 

 turning the oar one way he raifed the veflel, by turning it 

 the other way he deprefl!ed it. 



A glafs tube eighteen inches long, and one inch in dia- 

 meter, ftanding upright, its upper end clofed, and its lower 

 end, which was open, fere wed into a brafs pipe, through 

 which the external water had a pafl'age into the glafs tube, 

 ferved as a water-gauge or barometer. There was a piece of 

 cork with phofphorus on it, put into the water-gauge. When 

 the veflel defcended the water role in the water-gauge, con- 

 denflng the air within, and bearing the cork, with its 

 phofphorus, on its furface. By the light of the phofpho- 

 rus, the afcent of the water in, the gauge was rendered vifible, 

 and the depth of the vefl'el under water afcertained by a 

 graduated line. 



An oar, formed upon the principle of the fcrew, was 

 fixed in the forepart of the veflel j its axis entered the vefl"el, 

 and being turned one way, rowed the veifel forward, 

 but being turned the other way rowed it backward j it was 

 made to be turned by the hand or foot. 



A rudder, hung to the hinder part of the vefl'el, com- 

 manded it with the greatefl: eafe. The rudder was made 

 very elaftic, and might be ufed for rowing forward. Its 

 tiller was within the velTel, at the operator's right hand, 

 fixed, at a right angle, on an iron rod, which pafled 

 through the fide of the veflTel ; the rod had a crank on its 



S f outfide 



