74 ANNUAL OF SCIENTIFIC DISCOVERY. 



described above, and constructed for the U. S. Navy. These peculiar- 

 ities or improvements are thus described in the Boston Herald : " One 

 of them is a water-tight compartment two feet in width, extending 

 around the whole body of the vessel. The water is pumped out of this 

 compartment when the monitor is at sea. This lightens her, and, hav- 

 ing less surface exposed to the water, she can move more rapidly. If 

 the monitor is preparing for action, the compartment is filled. This 

 sinks her deeper into the water, so that little of the vessel, if any, ex- 

 cepting the turret, is visible. Outside of the water-tight division is to 

 be four feet of wood, and outside of the wood five inches of iron-plate. 

 To obviate the foul bottoms to which iron ships are liable, an oak bot- 

 tom is to be bolted on the iron one, and to be coppered like those of or- 

 dinary wooden vessels. They carry propellers and are provided with 

 two screws, one under each counter, by which they can be turned in a 

 smaller circle and in much less time than by a single screw." 



The Comanche. This vessel is one of the Ericsson monitors, and the 

 circumstance particularly noticeable about her is, that she was con- 

 structed in Jersey City, N. J., put together perfectly upon the stocks ; 

 and then taken apart and conveyed to San Francisco, California, where 

 she will be reconstructed. This feat of taking apart a ship of the size of 

 the Comanche (200 feet) has never been attempted before, and was emi- 

 nently successful in this case, every bolt being put in its place before a 

 single particle of the hull was taken down. The armor-plating of the 

 Comanche is composed of five courses of plates, having an aggregate of 

 five inches thickness. 



Sheathing for Iron-dads. - - Some very interesting practical experi- 

 ence has lately been gained in England in the use of paints for iron- 

 clad vessels ; also in the use of brass sheathing to prevent their bottoms 

 from becoming foul. The large armor-frigate, Black Prince, after 

 having; been five months in the water, was recently docked at Devon- 



c? ' 



port and her bottom examined. It had been coated on one side with 

 a paint chiefly composed of oxide of copper, and on the other with one 

 partly composed of the sulphate of copper. Both sides were corroded, 

 but the sulphate of copper was the cleanest ; still there were thousands 

 of barnacles adhering to the plates on both sides. The Resistance, 

 another smaller armor-frigate, was docked at the same time, but it had 

 not been in service quite so long. One of its sides had been covered* 

 with the oxide of copper paint, and the other with another paint, the 

 composition of which has not been published ; along the bottom also 

 several patches had been covered with thin porcelain plates cemented 

 with marine glue. It was found that most of these plates had dropped 

 off, the glue not being capable of holding them, and the rest of the bot- 

 tom was nearly as foul as that of the Black Prince. But the most re- 

 markable case was that of the Royal Oak, which was also docked at 

 the same time. This was a wooden vessel which had been originally 

 designed for a line-of-battle ship, but was afterwards plated with iron. 

 A band of lead was then run around the whole vessel below the deep- 

 load line, below which the vessel was sheathed with Muntz metal, 

 the common brass sheathing, containing about sixty per cent, of copper 

 to forty of zinc. The iron plates were painted with red lead ; and it 

 was supposed that the intermediate lead band, coated with paint, 

 would prevent contact and galvanic action between the iron and the 



