COMPASS IN IRON ARMOUR-PLATED, IRON, AND COMPOSITE SHIPS. 623 
On again referring to the paper “ On tlie Magnetic Character of the Armour-plated 
Ships, &c.,” of 1865, we read at page 275, “ D and E do not change with a change of 
geographical position.” 
As regards 2) this is fully confirmed by the results in the tables. Time alone 
appears to cause a gradual change in this coefficient during the first two or three 
years after launching, after which it remains remarkably permanent. 
Coefficient (S has no real value in the ships under discussion. 
Coefficient X. 
X= Iff-—y— is a factor generally less than 1, giving the northern component of the 
u 
mean directive force of the needle, or “ mean force to north.” 
X, as might be expected from its close connexion with '£), appears to be affected 
solely by lapse of time similarly to X>; for example, in the “ Malabar” (a sister ship to 
the “ Euphrates” of the tables), a valuable series of observations was made between 
England and Bombay, 4 ' the results of which are here recorded. 
\. 
Malabar.—Spithead, 17 vi. 67 . . . . ‘861 
Aden, 10 i. 70 . . . . -861 
Bombay, yy ii. 70 . . . . ’906 
Suez, xi. 70 . . . . '907 
Spithead, 5 ix. 71 . . . . '932 
Spithead, 28 x. 78 . . . . '930 
Each of the above values of X is the mean of several observations conducted under 
favourable circumstances, and the observations, as far as they go, confirm the conclu¬ 
sions drawn from other ships in England. The ship’s visit to the heat of the tropics 
seems to have accelerated the change in X. 
Coefficient /r. 
l+&+2> in which k represents the vertical force caused by vertical induction in 
the soft iron of the ship; It the vertical force from the hard iron. 
The values of p, contribute largely in many ships to the heeling error. For the 
purpose of eliminating the values of k from B, observations in widely different magnetic 
latitudes are still required. 
* By Staff Commander J. C. Richards, R.N. 
4 L 2 
