CHARACTER OE THE ARMOUR-PLATED SHIPS OE THE ROYAL NAVY. 289 
Lisbon for the purpose of cleaning the bottoms, to swing them at the same time, and 
the heeling coefficients so obtained correspond very satisfactorily with those obtained 
in England from observations of horizontal and vertical force. But, unfortunately, at 
present we have no instances in which the horizontal and vertical forces were observed 
at the time and place at which the ship was heeled and swung; and it seems very 
desirable that the theory should be put to the practical test, though there seems no 
reason to doubt that the results of the two methods would agree within the limits of 
errors of observation. 
9- 
g is one of those quantities which it is of importance to be able to estimate with some 
approach to accuracy, in order that the value of the mean vertical force, or p, may be 
determined by observations of the vertical force made with the ship’s head on one point 
only. 
The Tables show that this may 3 be done ; g, as might be expected, is larger the 
nearer the stern the Standard Compass is placed, and is negative in compasses placed 
near the bow. 
Achilles +‘194 
Resistance +T76 
Defence +T57 
Black Prince +T18 
Warrior + -069 
Achilles (Standard forward) . . — T72 
There are indications of changes in the value of the heeling coefficient and in the 
value of g from the lapse of time, corresponding to the changes in the values of 
2) and X; but more extended observations are necessary to show the amount and law 
of these changes. 
To afford a clear view of the general structure of the armour-plated ships, and the 
position of the several compasses, profile sketches of these ships are given (Plate XI.), 
and it may be deemed of sufficient interest to add a brief description of their general 
arrangements as affecting their magnetic characteristics. 
The Warrior, Black Prince, and Achilles, of 6100 tons, are types of the largest size 
iron-built and iron-plated ships of war ; they are 380 feet long, 58 feet beam, 26 feet 
draught of water, propelled by engines of 1250 horse-power, and carry from forty to 
twenty heavy guns. 3750 tons of iron is used in the construction of the hull, which 
varies in thickness from 1^ inch near the keel to f inch behind the armour-plates. 
For the Achilles 1200 tons of iron 4^ inches thick was employed for the armour-plating. 
The Hector and Valiant of 4100 tons, and the Defence and Resistance of 3700 tons, 
are types of the medium and smaller-sized iron-built and iron-plated ships of war. In 
the general features of construction they are similar to the Warrior, Black Prince, and 
Achilles ; all are frigate-built, or with a main deck for the principal battery of guns, 
2 r 2 
