CHARACTER OF THE ARMOUR-PLATED SHIPS OF THE ROYAL NAVY. 321 
20. In the construction of iron-built and iron-plated ships, regard should be had to 
the providing a suitable place for the Standard Compass. It is not difficult for any one 
who has studied the question, to suggest arrangements which would greatly mitigate the 
injurious effects of the iron of the ship ; the difficulty is to reconcile them with the 
requirements of construction and of working. 
Postscript. 
Since the foregoing paper was read, additional observations of deviations have been 
made in the Achilles and Defence, and observations in two new iron-built armour-plated 
ships, the Minotaur and Scorpion, the results of which are contained in the annexed 
Table. The observations in the Achilles show a continued diminution in the value of 
S3 and a continued tendency in 6 to return to its original value. The Defence con- 
tinues to show great permanence both in 93 and (5. 
The Minotaur, of which it has been thought desirable to give a woodcut drawn to 
the same scale as the ships represented in Plate XI., illustrates in a very remarkable 
manner some of the principles deduced from other ships. The Minotaur is the first 
iron-built ship completely plated from end to end ; her quadrantal deviation is con- 
sequently small. Having been built and plated head north, the original deviations in 
all the compasses were very large. In the steering and poop compasses the maximum 
deviation was above 60°. With deviations of this amount the compass becomes useless 
unless corrected by magnets, and magnets were consequently applied, which removed 
almost entirely the semicircular deviation. Probably in a very short time we shall find 
the original — 93 of these compasses to have so far diminished that the compasses will 
be found to be greatly over corrected and to have a considerable +93. Magnets were 
also applied to the Standard Compass. The heeling error at the poop compass is very 
large, 2° 46'. This arises from the compass being so near the stern of the ship, built 
and plated head north, and also from its being elevated above the armour-plating. It 
is interesting to contrast it with the heeling error of the steering compass, where from 
the peculiar configuration of the armour-plating being such as to give a — Jc, the heeling 
error is diminished and of a moderate amount. 
The Scorpion is a remarkable instance of the change which takes place in the semi- 
circular deviation from a change of position in a new iron-built vessel. Having been 
built head N. 76° W., or S. 254° E., the original value of 93 was — ’246, and the original 
starboard angle was 233-|°. After lying four months head S. 47° W. or S. 313° E., the 
value of 93 changed its sign and became +‘225, and the starboard angle increased to 
303A°, thus following very nearly the direction of the south line in the ship. The 
Scorpion is an instance of the successful correction of the heeling error by means of a 
vertical magnet. This reduced the heeling error from 1° 38' to 2 ; for each degree of heel. 
2x2 
