368 EXPLANATION OF THE PLATES. 



Beats Vesper . . . . . . 10 minutes. 



Diamond 12 



Gem ....... 5 



Against tide from Gravesend to London all other boats from 30 to 60 minutes. 

 For further information, see description of Plate XCIX. 



PLATE XLI. 



SECTION OF ONE OF THE ENGINES OF THE DON JUAN, PENINSULA 



COMPANY'S PACKET. 



The Don Juan was built by Messrs. Fletcher and Fearnall, of Limehouse, in 1836. 

 She was sailed round to Glasgow, where her engines were put in by Messrs. Claud, 

 Girdwood, and Co., the makers. On her first return voyage from the Mediterranean to 

 London, she unfortunately struck on the Tarifa point and went down in deep water. 



PLATE XLII. 



BOILERS OF HER MAJESTY'S SHIPS HERMES, SPITFIRE, AND FIREFLY. 



The drawings represent a front view and sections of boilers recently constructed 

 by the Butterly Company, who are now making a spare set to be used for any one 

 of the three vessels which may first require them. These boilers are very compact, 

 light, and efficient, and any two of them may be employed in case of accident to 

 one of them, when the vessel is at sea. Each has its own steam-pipe, which can be 

 shut off at pleasure, its safety valve, and a damper, which being closed, as shewn in 

 the transverse section, cuts off the communication with the chimney. A contrivance 

 is effected by which a man can creep into the boiler underneath the flues to clean or 

 repair it, which has been found very useful ; it does not increase the height of the 

 boilers, and adds very little to their weight. The front view of the boilers is placed 

 in a section of the Hermes, to shew " the channels " or passages by which the man 

 has access to the under side of the flues, down between the engine sleepers or 

 foundation timbers. 



The cylinders of the Firefly are 43^ inches in diameter, and the stroke is 4 feet 6 

 inches, which, at 22 revolutions per minute, gives the velocity of piston 198 feet per 

 minute. The area of the piston in square inches is I486'!, and if the effective pres- 



14861 x 198 

 sure be 10 Ibs. per square inch, it would make the horses' power 33000 = ^ 



