ON THE THREE REPORTS OF THE LIVERPOOL COMPASS COMMITTEE. 97 
The first Report was merely preliminary, and stated the steps which the 
Committee were taking to obtain information. One of the few points on 
which the Committee had made observations, the details of which they give, 
was the direction of the neutral lines, or of those lines in the iron structure 
of the ship which separate the parts in which the iron attracts the north end 
of the compass-needle from those in which it attracts the south end. Theso 
observations, we may observe, though to a certain extent useful as enabling us 
to see generally the nature of the action of the body of the ship on the com- 
pass, do not give any very definite results, from the transient induced mag- 
netism being even more mixed up with the permanent or subpermanent 
magnetism than in the case of ships “‘ swung.” 
The Committee, in the first Report, draw the following inference from these 
observations, viz. that “the diverse direction of the magnetic lines appears 
to countenance Dr. Scoresby’s supposition that they depend on the position of 
the ship when building.” 
The second Report contains the results of much more extended observa- 
tions and matured views. On the point of most marked importance—the 
connexion of the magnetism of an iron ship with her position when building — 
the Committee had now arrived at a definite opinion. They say :—“ The 
records of the Committee no longer allow a doubt as to the connexion 
which exists between the direction of a ship’s original magnetism and her 
position when upon the building-slip. In all the ships which haye been 
examined, the north end of the compass-needle invariably deviated towards 
that part of the ship which was furthest from the north when she was build- 
ing, if the compass was placed in a central position and free from the influence 
of individual masses of iron.” * 
The attention of the Committee was also directed to the changes which 
the deviations undergo shortly after an iron ship has been launched, and they 
came to the conclusion that the subpermanent magnetism undergoes consider- 
able changes at and immediately after launching, and during the first voyage ; 
but that after this early reduction of a ship’s magnetism has taken place, the 
remaining portion appears to be comparatively permanent. This, however, 
is subject to the qualification mentioned in the Report, and which may be 
stated as follows :—that when a ship has been for a considerable time in one 
position or on one course, the induced magnetic state acquires a certain degree 
of permanence which modifies the previous subpermanent magnetism. The 
general effect of this, it will be easily seen, is upon a change of course to 
cause the vessel to deviate from her course, by dead reckoning, in the direction 
of her previous course. 
In this Report attention is called to the very important subject of the 
variation of the directive force in iron ships on different points of the com- 
pass. With reference to this, it may be observed, that we think it is'a result 
of the observations generally, that the degree of correctness of observations of 
force is much inferior to that of observations of deviation. The observations 
of deviation give, by theory, the proportions of the directive forces on the 
* We have distinguished by italics the last part of this sentence in order to draw atten- 
tion to one circumstance which continually forces itself into notice in the perusal-of the 
Reports, viz. the very little attention which is paid in the mercantile marine to the selec- 
tion of a place for the compass. In these ships the compass is constantly placed so near 
iron sternposts, spindles of capstans, bulkheads, roundhouses, spindles of wheel, &c., 
that the effect produced on the compass is not only extravagantly large, and the rapidity 
of variation of the force in the field very great, but the effect produced is in truth not so 
much that caused by the ship considered as a whole, as that caused by the particular 
masses of iron in the vicinity of the compass, 
1862, i 
