COMPASS IN IRON ARMOUR-PLATED, IRON, AND COMPOSITE SHIPS. 621 
Looking to this result, it hardly seems probable that vertical induction in soft iron 
should be slower in its action, and require perhaps days for full development. 
Among the iron armour-plated ships of the tables we have, in the case of the 
“Triumph” and “ Swiftsure” (two sister ships), experimental evidence that there is 
no sign of “ lagging” in the changing part of their deviation, but that it alters directly 
as the tangent of the dip for any given position of the ship. 
Both vessels, from requirements of the service, have their standard compasses placed 
unusually far from the stern, in a position 13 feet from the top of an armour-plated 
transverse bulkhead 5 inches thick. These ships were swung in the course of a few 
successive months, the observed deviations in each case but one corresponding with 
the dip at the locality, the values of which were as follows:— 
Triumph . 
Swiftsure . 
Range of 9 82°. 
r+6? 
| +17 
< -n 
] -29 
L -52 
° 
> Range of 9 119 
I 
J 
O 
To proceed with the constants c and f 
The values of c are very valuable, not only as a means of predicting the probable 
change of deviation for the particular ships in which they are known, but also for ships 
of similar construction. As an illustration of the similarity of this constant in certain 
ships, the following examples are given where sister ships are bracketed:—• 
Triumph. 
c. 
+ •106 
Swiftsure. 
+ •110 
Northampton. 
-•021 
Nelson. 
-•014 
Shah. 
-•005 
Raleigh. 
-•006 
Comus. 
+ •034 
Cleopatra. 
+ •032 
Carysfort* ....... 
+ •044 
Boxer. 
+ •023 
Pert. 
+ •026 
Firefly. 
+ •005 
Wrangler. 
+ •002 
* The “ Carysfort” is a sister ship to “ Comus” in every respect, with the exception that the former 
has no vertical iron shaft through which the screw is raised. In the “ Comus” and “ Cleopatra” this 
shaft is 30 feet from the compass. 
mdccolxxxiit. 4 L 
