Deviations of the Compass on Iron and Wooden Steam-ships. 538 
known as the “ quadrantal”’ deviation, shows, that while in wood- 
built steam-ships it seldom exceeds 1° or 13°, it rises in iron-built 
ships from 13° to 6° and 7°; the Liverpool Compass-Comiittee 
recording even a point of the compass. ; 
The chief characteristics of the quadrantal deviation, as developed 
in this investigation, are— 
1. That it has invariably a positive sign, causing an easterly 
deviation in the N.E. and 8.W. quadrants ; and a westerly deviation 
in the S.E. and N.W. quadrants. 
2. Its amount does not appear to depend on the size, or mass of 
the vessel, or direction when building; or on the existence of iron 
beams. 
3. That a gradual decrease in amount has occurred, after the 
lapse of a number of years, in nearly every vessel that has been 
observed. 
4, That the value remains unchanged in sign and amount, on 
changes of geographic position. 
5. That a value not exceeding 4°, and rangmg between that 
amount and 2°, may be assumed to represent the average or normal 
amount in vessels of all sizes. 
Numerous examples are given in support of these propositions, as 
also of the uniformity of the amount of quadrantal deviation when 
determined in various parts of the ship; and, assuming the normal 
amount in iron steam-ships as from 2° to 4°, an analysis is given by 
which it is seen that 75 per cent. of the iron ships of the Royal Navy 
are included in this condition. 
Two questions of importance here arise ; are the results of this ana- 
lysis conclusive, and if so, under what conditions do large quadrantal 
deviations occur? Reverting to the Astronomer Royal’s early experi- 
ments in 1838-39, in the iron ships ‘ Rambow’ and ‘Ironsides,’ whose 
values were very small, and presuming that those vessels were built. 
of good material—from their then experimental character—as also 
that similar conditions of material of good quality exist in the iron 
ships of the Royal Navy, it is assumed that the value (2° to 4°) re- 
presents the average condition of a ship built of the best or superior 
Iron. 
On the other hand, can the inference be drawn that large quadrantal 
deviation in an iron ship implies that inferior material has been used 
in her construction? Attention is here directed to the ships ‘ Birken- 
head’ and ‘ Royal Charter,’ which from their well-known magnetic 
coefficients may be regarded as the types respectively of ‘hard’* 
and ‘soft’? iron constructed vessels, and from their consideration, 
as also from a review of the general results, these conclusions are 
derived :— 
1. That in an iron ship of ordinary dimensions, a standard com- 
pass can be placed, the deviations of which will but httle exceed those 
obtaining in wood-built steam-ships ; and further, that on changes of 
geographic position, however distant, these deviations will be within 
smaller limits, and can be approximately predicted. 
2. A divergence from these conditions will arise when the inductive 
