274 PROSPECTS OF STEAM NAVIGATION. 



commodations for passengers. Under that, the second or freight deck, also 

 clear of machinery from stem to stern, is occupied by the cargo ; and beneath 

 this again, buried in the very bottom of the vessel, is the mechanical power of 

 propulsion occupying, however, only about one fifth of the space below the 

 freight-deck. The square tunnel we have referred to for the discharge of 

 the gases, and the ventilation of (lie engine-room, is carried up through the 

 decks and stands in one of the saloons, but presents no other appearance to 

 the eye than that of a pillar five feet square, handsomely empannelled and 

 decorated, and adorned with mirrors. The freight-deck being interposed be- 

 tween the cabins and the machinery, intercepts all noise and vibration. 



When this mode of propulsion is applied to vessels-of-vvar, as in the case of 

 the Princeton, there is still another object to be accomplished. It is desirable 

 that the whole of the machinery should be below the water-line, so as to be 

 effectually protected from shot. This is accomplished by engines of a peculiar 

 construction, invented and patented by Captain Ericsson, which have been 

 worked with complete success in the Princeton. A representation of these, 

 in transverse vertical section, is given in fig. 7. It consists of two semi-cylin- 

 ders, presenting their semicircular sides downward, and being flat at the top. 

 They are placed beside each other above the main shaft, having their axes 

 parallel to it and to the keel. The ends of the axes are represented at A B. 

 To these axes are attached vibrating rectangular planes, which move alter- 

 nately from left to right, and right to left, within the semi-cylinders, and in 

 steam-tight contact with them. These planes are attached to the axes of the 

 cylinders, the ends of which appear at A and B, so that the vibrating motion 

 of the planes will impart a corresponding motion to the arms A E and B F, 

 attached to the ends of the axes A and B. The ends of these arms E and F 

 are attached to two connecting-rods, E D and F D, which are both attached to 

 the crank S D, which drives the main shaft. 



The steam is admitted a> ernalely to each side of the vibrating planes with- 

 in the semi-cylinders, being at the same time withdrawn from the other side 

 by a condenser. 



The action of the connecting-rods on the crank will be best understood by 

 following them successively through their various positions. In fig. 8, the 

 rod F D is in the position in which it has no power on the crank ; but the 

 rod E D, being at right angles with the crank, has full effect upon it. The 

 crank therefore moves from the position represented in fig. 8, to the position 

 represented in fig. 9, where the rod E D becomes powerless. The crank is 

 then driven to the position represented in fig. 10, where the rod D F becomes 

 again powerless, and E D is effective. The crank is then moved to the posi- 

 tion represented in fig. 11, where E D is powerless and F D effective, and 

 so on. 



Thus it appears by this arrangement that the relative positions of the crank 

 and connecting-rods are such as to exercise a uniform action on the main shaft. I 



The space occupied by the machinery in the lower part of the stern of the ) 

 vessel, is surrounded by fuel, as represented in figure 7, and the whole is , 

 considerably below the water-line W. 



This machinery is designed only for war-vessels. Its construction and op- 

 eration are somewhat too expensive to be used for the mere purposes of com- 

 merce, where the advantages of its being placed below the water-line are of no 

 account. 



The steam packet-ships to which we have referred are calculated to make 

 an average speed of nine statute miles per hour when in full operation. It is 

 computed that they can maintain the communication between New York and 

 Liverpool with regularity and despatch the average western passage being 



