347 
diurnal variation of the magnetic needle^ &c. 
of that at s’* P. M. above it was *00177, and the excess of the 
maximum above this was *00049. So that the theory agrees 
in all respects as nearly with these observations as can pos¬ 
sibly be expected. I may also notice that the mean of seven 
months’ observations by Professor Hansteen, at Christiania, 
where the variation was about 20® west, gives the minimum 
intensity at lo’* 30™ A. M., and the maximum of the recorded 
observations 7** P. M. : the maximum appearing however to 
happen somewhat later. It may be proper to add, that the 
method I adopted for determining the diurnal changes in the 
intensity of the horizontal needle was totally dissimilar to 
that employed by Professor Hansteen. 
Although I have hitherto but slightly noticed the observa¬ 
tions made at Port Bowen, I nevertheless fully appreciate 
those observations, and the zeal and ability of the observers. 
As might have been anticipated from the law to which I have 
referred, as connecting the deviations of the horizontal 
needle with those of the dipping needle, the extent of the 
daily variation observed at Port Bowen was such, that had 
the changes taken place with any degree of regularity, the 
times at which the maximum east and maximum west devia¬ 
tion occurred, would have been determined with great pre¬ 
cision. This however was by no means the case, and such 
irregularities take place, from day to day, in the extent 
of the variations, in the times of their maxima, and in 
the times of maximum and minimum intensity, that it ap¬ 
pears to me, these irregularities must be the effects of local 
causes, equally irregular in their operation, unless we admit 
that from the peculiarity of the situation, the dip being above 
88®, irregularities, which in other cases completely elude 
