IN THE lEON SHIPS OE THE EOTAL NAVY. 
351 
sarily inductive material running nearly fore and aft the vessel, I am disposed to attach 
but little comparative value to any of the results except those of the Admiralty 
Standard compass, as it will be seen that the other compasses are influenced by the 
near proximity of steam funnels or iron masts. 
Directing attention to the changes in the magnetism of the ship as indicated by this 
compass, the gradual diminution of the ship’s force is marked at each successive period 
of observation, and also the constant tendency to attain a fore-and-aft direction. In the 
first five days, from Deptford to Portland, the force had diminished from 0-585 to 0-480, 
nearly one-fifth, or the semicircular deviation decreased from 35° 50' to 28° 45'; the 
direction of force, or neutral points, approaching a fore-and-aft line 10°, or from 47° on 
the starboard bow to 37° : it is here worthy of remark, that the general direction of the 
ship’s head for three days at Portland out of the five named, was N.W., or exactly 
opposite to her direction whilst lying at Deptford. 
The change at the expiration of the next six weeks, the ship in the interim having 
made the passage to Holyhead, with some trifiing rough weather, still shows a diminu- 
tion of force, and tendency to the fore-and-aft direction of the neutral points of disturb- 
ance: the former is reduced from 0-480 to 0-390, or about one-sixth (the corresponding 
semicircular deviation being 28° 45' and 23° O'); and the latter changed 5°, or from 37° 
to 32°. 
The changes denoted by the mast and platform compasses do not follow the same 
progressive decrease and change of direction of ship’s force. To the less perfect obser- 
vations of the mast-compass, arising from the difficulty of obtaining readings. aloft, and 
from the friction of blunted pivots after a few weeks’ wear and tear, can be traced the 
probable causes for this instrument ; the unfavourable but unavoidable position for the 
platform compass has been adverted to. 
The quadrantal deviations of all the compasses show a decrease, so far confirmatory of 
the law that exists in the numerous vessels reviewed ; but there is an anomaly detected 
by Mr. Aiey * in the quadrantal disturbance of the Admiralty Standard compass worthy 
of record, viz. that it is larger in the quadrant from west to north ; the position opposite 
to that in which the ship was built. 
1st, or 
2ud, 
3rd, 
4th, 
N.E. quadrant. 
S.E. 
S.W. 
N.W. 
River Thames . 
o / 
. -f 4 33 
o / 
-2 40 
O i 
-f-4 8 
O / 
-6 6 
Portland . . 
. +4 38 
-3 8 
+ 4 53 
-6 37 
Indication of rapid changes in the ship’s magnetism was also given by the ship’s esta- 
blished standard compass, which had been compensated on the passage down the river 
Thames (from the known direction of the ship’s head by astronomical bearings), and 
deemed by the gentlemen engaged for the purpose as correct. At Portland, with liead 
in the N.W. direction, it had 7° error on the second day at that anchorage. 
* Communicated in a letter to Mr. Etjndell, Secretary of the Liverpool Compass Committee. 
