184 Lieut . Foster’s comparison of the diurnal changes 
of the world lies between the magnetic pole and the sun, 
then it follows, that in some certain number of years the 
magnetic north pole will perform a revolution from east to 
west round the pole of the earth, and produce an annual 
change in the variation of the compass in that direction, which 
is known to obtain. That this may be the case, is rendered 
probable, by considering that the sun at present approaches 
nearer to the magnetic north pole in its southern, than in its 
northern passage over the meridian, by twice the north polar 
distance of the magnetic pole ; and although the reverse 
takes place on the south pole, yet, as the sun is longer on 
the northern than on the southern side of the equator, there 
will be a preponderance of action to carry the north pole for- 
ward to the westward, and consequently the south pole to 
the eastward, as is supposed to be the case by many eminent 
philosophers in this country. 
However, these observations will, of course, require to be 
repeated in other parts of the world, before this hypothesis 
can be considered as fully confirmed by experiment. 
In this concluding communication relative to our recent 
northern magnetic experiments, I beg leave again to express 
my obligations to Mr. Barlow and to Mr. Christie. To 
Mr. Christie, for his kindness in permitting the observations 
on the dip and magnetic intensity to be made in his garden at 
Woolwich, and for the valuable assistance he rendered me in 
the equipment of the magnetical instruments supplied to the 
Expedition. To Mr. Barlow, I stand indebted in a manner 
which I find it difficult to describe ; indeed it is no more than 
due to the scientific liberality of this Gentleman to state, that 
on many occasions, when I have shown him my experiments 
