CHARACTER OF THE ARMOUR-PLATED SHIPS OF THE ROYAL NAVY. 279 
From these results we may infer that the process of plating an iron ship in the direc- 
tion opposite to that of building will always produce a diminution, which in some 
cases may become a reversal of her semicircular deviation ; and that by duly taking 
advantage of this circumstance, the deviations of iron-plated ships may be brought within 
manageable limits. 
The Tables show, as might have been anticipated, the much larger amount of the 
deviation in the steering and main-deck compasses than in the Standard Compass, and 
the advantages to be derived from a judicious selection of a place for the compass ; un- 
fortunately even in the case of the Standard Compass the choice of position is so limited 
by the exigencies of the arrangements for working and fighting the ship, that the devia- 
tions in these compasses are generally larger than could be wished. 
2. After launching, and when the vessel is swinging at anchor, or sailing or steaming 
in various directions, the values of B and C generally diminish rapidly ; and this change 
would no doubt be accelerated by the vessel being exposed to blows or jars in a position 
different from that of building. 
The following cases show a rapid change of B and C after launching. The most 
instructive have been selected from the Tables, but the elaborate series of observations 
made in the Great Eastern (Phil. Trans. 1860) are the most conclusive, as that ship was 
in every respect prepared for sea, and the observations are strictly comparable throughout. 
H.M.S. Achilles, built in dry dock at Chatham, and fully plated there also, head 
S. 52° E., floated out of dock 24th December 1868, and moored head and stern in 
the River Medway, head S. 62° E. In March 1864, after taking in steam machinery, 
the ship made a short trial trip down the river, and then returned to the former 
moorings, but with her head secured in the opposite direction, or N. 62° W. 
Equipment and fittings completed by October 11th, when the head was shifted 
round to S. 55° E., and on the following day steamed to Sheerness and commenced 
sea service. 
23. 
1863. 
Dec. 
23. — In dock at Chatham 
+ ■464 
+ •323 
1864. 
Sept. 26. — Complete for sea, head N. 62° W. . . 
+ •377 
+ •037 
Oct. 
11. — Complete for sea, head S. 55° E. . . 
+•355 
+ •062 
Oct. 
13. — Swinging at anchor, Sheerness . . . 
+ •362 
+•047 
Dec. 
5. — At Plymouth, after 25 days in dock,) 
- + *361 
+ •123 
head S. 79° E J 
H.M.S. 
Royal Oak, wood-built ship, iron-plated in dock at Chatham, 
head S. 49° E„ 
1863. 
Mar. 
19. — Floated out of dock 
+ •253 
+ •287 
April 11. — Swinging at anchor, River Medway . 
+ •231 
+ •197 
June 
2. — Swinging at anchor, River Medway . 
+ •248 
+ •128 
1864. 
Jan. 
8. — Swinging at anchor, Plymouth . 
+ •218 
+ •172 
The example of the Achilles is very instructive. The large value of (S+’323 giving 
mdccclxv. 2 Q 
