H4< Ca.pt. Sabine on irregularities observed 
experiments in ships under their direction at the principal sea 
ports, with a view to ascertain if compasses were similarly 
affected in other ships, and to try the general applicability of 
rules which he had found useful in correcting the errors in 
the Investigator. These rules, with the observations and 
reasonings on which they were founded, were published in a 
short paper in the Philosophical Transactions, and in a more 
detailed form in Appendix No. II. in the Voyage to Terra 
Australis. There are three points in these statements chiefly 
worthy of attention, from their practical importance ; and on 
which it seems desirable, therefore, to notice how far his 
observations have been confirmed by those made in the 
Isabella and Alexander. 
First ; he found that in every ship a compass would differ 
very materially from itself, on being removed from one part 
of the ship to another. Experience of this source of irregu- 
larity, had induced him early in his voyage, to confine the use 
of the compass, with which his survey was carried on, to one 
particular spot. The place he selected was determined by 
convenience in other respects ; it was on the binnacle, and 
exactly amidships. 
The Isabella and Alexander had not completed half their 
voyage across the Atlantic, before it was found that the 
binnacle compasses of the one ship differed very materially, 
in indicating the course steered, from those of the ocher: 
namely, one point, or n£°. No dependance whatsoever could 
be placed on the agreement of compasses in different parts 
of the ship, or of the same compass with itself, if removed 
but a few inches : even in the neighbourhood of the binnacles 
the variation, as observed amidships, was from 8° to io° 
