PREFACE. 
IX 
the magnetic maps now in construetionj the principal 
part of the materials for that quarter of the globe. 
“ Having made some progress in reducing these, I 
have had frequent occasion to admire the scrupulous and 
persevering attention which you paid to all those minute 
circumstances on which, in observations of this nature, 
the accuracy of the results is mainly dependent ; and 
which is the more important in your case, because the 
interior of the continent of Africa is altogether without 
such determinations, and the direction of the magnetic 
lines is consequently more than usually dependent for 
its correctness on the accuracy of the observations on the 
coasts. I need scarcely say, that the peculiar objects 
and circumstances of your Expedition, and the sufferings 
which it underwent, render such careful attention to 
minutiae the more worthy of admiration. The co- 
ordination of your observations on Term- day with the 
simultaneous observations made in different parts of 
the globe, is also in progress, and promises to afford 
some interesting and valuable results, particularly the 
Term-day of April, 1842, which you observed at 
Fernando Po. It was a day of considerable magnetic 
disturbance apparently over the whole globe, and 
Western Africa seems to have had its full share, 
Fernando Po, as a station, is well placed, in con- 
nection with the surrounding stations of the Cape 
