98 REPORT—1862, 
different courses. Each observation of force, therefore, when compared with 
the proportionate force derived from the deviations, gives a value of the factor 
(A) by which the forces derived from the deviation ought to be multiplied. 
« The second Report of the Liverpool Compass Committee also mentions 
the interesting fact, which has been completely verified in the ships of the 
Royal Navy, that the quadrantal deviation of all ships is, with very rare and 
special exceptions, positive, or such as to cause a deviation of the north end 
of the compass ¢o the north end of the ship and from the north side of the 
ship, Such a deviation might be caused by an attraction to the north end or 
a repulsion from the north side. We may distinguish between the two 
causes by observing that the former would increase, and the latter diminish, 
the mean directive force of the needle, Observations of the directive force, 
therefore, show from which cause this deviation arises, and indicate that m 
general in iron-built ships the quadrantal deviation is principally caused by 
the repulsion of the north side of the ship, the north end of some ships attract- 
ing the north point of the needle, of others repelling it, but in almost all 
such ships with a force inferior to that of the repulsion of the north side. 
In wood-built ships the case is different: there is no transverse horizontal 
iron to cause repulsion from the sides; and the positive quadrantal deviation 
is caused by the attraction of the masses of iron before and abaft the compass. 
The exceptions are generally in the case of wooden screw-streamers, when the 
screw-shaft, passing through the place of the compass, causes a repulsion 
from the north end, or in the case of elevated compasses, in which the original 
+D has depended on an excess of repulsion of the sides over the repulsion of 
the ends. As the compass is elevated, the direction of the former force, be- 
coming more oblique, loses its effect much more rapidly than the latter, and 
the D consequently changes its sign. 
The Committee also observed on the heeling error, and on the general 
tendency being to draw the north end to the weather side, but stated that the 
evidence which they had obtained did not enable them to draw any definite 
conclusions on this subject. 
The third Report embodies the results of very extended and varied obser- 
vations, leading to very definite conclusions, which may nearly to the full 
extent be accepted as being now established. 
As we have already observed, the present state of the mathematical theory 
is such, and the mathematical results coincide so exactly with observations, 
that the details of observation lose much of their interest, and the results 
involved in the coefficients extracted by rule from the observations are suf- 
ficient for all practical as well as theoretical purposes. 
The Report commences with a summary of the points which the Committee 
consider as established; they are— 
1. That the magnetism of iron ships is distributed according to precise 
and well-determined laws. 
2. That a definite magnetic character is impressed on eyery iron ship 
while on the building-slip, which is never afterwards entirely lost. 
3. That a considerable reduction takes place in the magnetism of an 
iron ship on first changing her position after launching, but afterwards 
that any permanent change in its direction or amount is a slow and 
gradual process. 
4. That the original magnetism of an iron ship is constantly subject 
jamal fluctuations from change of position arising from new magnetic 
inductions, 
