C *** 3 
VIII. On Irregularities observed in the direction of the Compass 
Needles of H. M. S. Isabella and Alexander , in their late 
Voyage of Discovery, and caused by the attraction of the iron 
contained in the Ships. By Captain Edward Sabine, of the 
Royal Regiment of Artillery, F. R. S. &c. 
Read February 18, 1819. 
It is proposed in this paper to show in what respects the 
effects of local attraction, in the above mentioned ships, were 
conformable to the observations which had been made in 
preceding voyages ; and how far the errors, which were 
found to take place on different courses, and under different 
dips of the magnetic needle, corresponded with the rules for 
calculating corrections, which Captain Flinders had found 
useful in his own experience, and which he had recommended 
for a more extensive trial. 
It may be desirable to premise, that the irregularities here 
alluded to, are not those accidental disturbances which may 
be caused by iron placed inadvertently too near the compasses; 
but the permanent, and constant effect of the mass of iron 
contained in a ship, affecting its compasses at all times, and 
in a greater or less degree, according as its influence is more 
or less powerful, in comparison to the directive force of the 
earth’s magnetism. That errors have always existed from 
this cause, may be inferred, from the uncertainty which ex- 
perience has attached to the results of azimuths observed in 
ships. The cause, however, appears to have been very long 
