XU 
INTRODUCTION. 
Sabine was assisted by Mr. Hooper, purser of the Hecla, a gentleman 
to whose' zeal and exertions, during a period of three years that 
we have been employed together on this service, I am more indebted 
than I can adequately express. By those who have been accustomed 
to the charge of chronometers for any length of time, and who 
know the weight and importance of that charge, it will be considered 
as deserving no small credit on the part of these gentlemen, that, for 
a period of nearly twenty months, during which, eleven chronometers 
were on board the Hecla, only two instances occurred of a single 
chronometer being suffered to go down by neglect. 
The observations for the variation of the magnetic needle, made on 
board the ships, have been altogether omitted in the course of the 
narrative ; because, until a correction for the effects of local attraction 
has been applied, they give little or no information as to the true 
amount ; the whole, therefore, have been referred to the Appendix, 
in the order in which they were taken. A number of these, obtained 
for the express purpose of ascertaining the amount of the ship’s 
attraction upon the needle, with her head placed in different di- 
rections, and when the dip and true variation were known, will be 
found useful, perhaps, towards establishing some general formula for 
the correction of those errors at sea. Such a formula, however, is 
the less important from the facility with which the amount of this 
irregularity may at almost any time be found, when the sun is visible, 
by taking azimuths on a north and south magnetic course, in order to 
obtain the true variation, and then upon any other required direction 
of the ship’s head. For the purposes of navigation, indeed, it is 
generally necessary only to ascertain the variation to be allowed on 
one or more courses, without regard to the true amount. This is par- 
