OF THE MAGNETIC DECLINATION AT POINT BAEROW. 
513 
of regularity in the decrease of the numbers on either side of the maximum is a very 
remarkable feature. The progression bears a very close resemblance and analogy to that 
of the ivesterly disturbances at Point Barrow, as seen in Table IV., and appears to have 
little or nothing in common Avith the progression of the easterly disturbances at Point 
Barrow in the same Table. 
The presence of aurora is however by no means to be regarded as an indication of the 
contemporaneous existence of a disturbance of sufficient magnitude to be admitted into 
the category of the “ disturbed ” observations of this paper. In the six months referred 
to, in which the aurora was recorded at 1079 hours, only 272 of the contemporaneous 
observations were, in this sense, “ disturbed,” and 807 were not so ; i. e. 272 out of 1079, 
or only about one-fourth of the observations made during the recorded presence of the 
aurora, differed as much as 22'’86 from the normal at the same hour and in the same 
month. 
Of the fact, that the aggregate amount of disturbance at Point Barrow, when compared 
AAith Toronto, greatly exceeds the calculation founded on the inverse proportion of the 
horizontal force at the two stations, there can be no reasonable doubt. To what is this 
disproportion OAAung 1 Is it, as some may suppose, that Point Barrow is situated nearer 
than Toronto to the locahty where the greatest intensity of disturbance is manifested 1 
If it be so, — and this, be it remembered, is a question Avhich admits of being ascertained 
by future investigations, similar to the present, at stations suitably chosen, — the question 
AA'hich will immediately present itself will be, by what peculiar physical or other conditions 
the locality of the greatest intensity of disturbance is distinguished. In the mean time, 
the widely dissimilar proportions of the disturbance-variation, and of the solar-diurnal 
variation, at Point Barrow and Toronto, supply additional evidence of the distinct law^s 
by Avhich the tAvo classes of phenomena are governed, and of the necessity of their being 
separately studied *. 
* The disturbances at Point Barrow do not appear to give support to a conjecture that has been recently 
expressed, that the “ occasional disturbances may possibly include two distinct classes of changes, obeying 
separate laws, one of them being strictly periodic and constituting a part of the regular diurnal change, 
whilst the other is strictly abnormal and simultaneous at different stations.” The regular diurnal change 
at Point Barrow has its greatest easterly elongation about 7 a.m., which is nearly the hour of the greatest 
westerly disturbance-variation ; and its greatest westerly elongation about 1 p.m., at which time the disturb- 
ances, both easterly and westerly, are nearly a minimum. The indications of the phenomena seem therefore 
to be as nearly opposed as can well be to the conjecture referred to. It is quite true that if the attempt be 
made to obtain the laws of the disturbances from observations from which the effects of the regular diurnal 
variation have not been previously eliminated, the laws so obtained will include “ two distinct classes of 
changes, obeying separate laws, one of them constituting a part of the regular diurnal variation.” But 
when suitable processes have been employed, by which the mean influence of the regular diurnal variation 
has been eliminated from the observations which are used in examining the periodic laws of the disturbances, 
and when the characteristic value of a large disturbance has been taken in proper proportion to the ordinary 
range of the diurnal variation, I have not found in any case an indication of an admixtm’e in the disturb- 
ance laws of an element corresponding in its turning-hours, &c. to the periodic laws of the regular solar- 
diurnal variation. — Sept. 5, 1857. 
MDCCCLVII. 3 X 
