DIFFERENT KINDS OF SHIPS. 89 



and 15 broad, and weighs 43 tons. They are tested at a pressure of thirty 

 pounds to the square inch. The ship can make from 8 to 10 miles an 

 hour without sails. The first cabin accommodates 142 passengers, and is 

 fitted up with great elegance. The main saloon is 85 feet long and 22 feet 

 broad. There are also a barber's shop and smoking-rooms. The galley 

 contains 575 square feet of surface and cooks for 400 persons. There is a 

 second cabin. In the lower hold there are large iron cisterns, from which 

 water can be carried to any part of the vessel by forco pumps. The 

 hold has 375 tons of stowage-room for merchandise. A special room is 

 appropriated to the mail. The Washington, although long since super- 

 seded both in swiftness and elegance by other ocean steamers, deserves 

 to be recorded as the pioneer of American Trans-Atlantic steam navi- 

 gation. 



It may be desirable under certain circumstances for one of the paddle- 

 wheels to work while the other stands still ; but as the axis with its crank 

 is of one piece, such an arrangement of the wheels would be impossible. A 

 special apparatus has consequently been invented, and is shown in pi. 18, 

 figs. 16 to 19. Fig. 16 is a side view. Jig. 17 a cross-beam of the appa- 

 ratus,^^. 19 a front view ; and^^. 18 a view from above after the removal 

 of the upper cap. The axis, O, the crank, N, and the cross-beam, M^, on 

 each side are of one piece, and to the cross-piece is attached the connect- 

 ing-rod, M, which, when moved by the engine, puts this part of the axis in 

 motion. The place of the second crank is supplied by the apparatus. A 

 cross-beam, M, is placed on a gudgeon resting on the screw-block, F, 

 which is covered by the plate, C, through which the screw, V, passes, in 

 order to secure the gudgeon, M' ; ff, are two screws, which tighten or 

 loosen the band, B ; the block, F, has cogs underneath, so that when the 

 band, B, is drawn tight it catches into the teeth of the disk, N, and makes 

 it revolve with it. As the disk, N, and the axis, O, are concentric, this 

 disk, as well as the axis, O , of the paddle-wheel, which is connected with 

 it, must revolve at the same time with O. But if the band, B, is loosened 

 by the screws, //, the disk, N, slides and becomes out of gear with F, and 

 consequently only the block, F, moves with the axis, O, while O' stands 

 still, until the screws, //, and hence the band, B, are tightened, and the 

 disk, N, is again brought into gear with F. 



We will now consider those steamships which have Archimedean screws, 

 or simply the screw-propellers, which have recently come into frequent use, 

 though it is not more than nine or ten years since the first experiments with 

 them were made. 



It was desired to simplify the propelling apparatus of a ship as far as it 

 could be done without diminishing the velocity, to avoid the risk of break- 

 ing the paddle-wheels, and to protect the motor of the vessel in men-of-war 

 from the enemy's fire, by which the wheel-houses were easily destroyed : 

 the Archimedean screw fulfils all these conditions. As early as 1768 it was 

 proposed by Paucton, a French mathematician, to propel a vessel by means 

 of the Archimedean screw, but he was only laughed at. This did not pre- 

 vent Delisle, an engineer in France, from entertaining the same plan in 



V41 



