300 Royal Society :— 
and advantage receive the appellation of “ occasional,” are, in their 
mean or average effects, subject to periodical laws of a very system- 
atic character ; placing them, as a first step towards an acquaintance 
with their physical causes, in immediate connexion with the sun 
as their primary exciting cause. They have—1, a diurnal variation 
which follows the order of the solar hours, and manifests therefore 
its relation to the sun’s position as affected by the earth’s rotation 
on its axis; 2, an annual variation, connecting itself with the sun’s 
position in regard to the ecliptic; and 3, a third variation, which 
seems to refer still more distinctly to the direct action of the sun, since, 
both in period and in epochs of maximum and minimum, it coincides 
with the remarkable solar period of about ten, or perhaps more nearly 
eleven, of our years, the existence of which period has been recently 
made known to us by the phenomena of the solar spots; but which, 
as far as we yet know, is wholly unconnected with any thermic or 
physical variation of any description (except magnetic) at the surface 
of the earth, and equally so with any other cosmical phenomena with 
which we are acquainted. The discovery of a connexion of this re- 
markable description, giving apparently to magnetism a much higher 
position in the scale of distinct natural forces than was previously 
assigned to it, may justly be claimed on the part of the Colonial Ob- 
servatories, as the result of the system of observation enjoined (and 
so patiently and carefully maintained), and of the investigation for 
which it has supplied the data; since it was by means of the disturb- 
ance-variations so determined, that the coincidence between the phe- 
nomena of the sclar spots and the magnitude and frequency of mag- 
netic disturbances was first perceived and announced (Phil. Trans. 
1852, Art. VIII.). 
The extent and mutual relation of the disturbance-variations of the 
three elements, even at a single station, supply a variety of points of 
approximation and of difference, which are well suited to elucidate 
the physical causes of these remarkable phenomena; but valuable as 
such aids may be when obtained for a single station, their value is 
greatly augmented when we are enabled to compare and combine the 
analogous phenomena, as they present themselves at different points 
of the earth’s surface. To give but a single example :—there are cer- 
tain variations. produced by the mean effects of the disturbances 
which attain their maximum at Toronto during the hours of the 
night ; the corresponding variations attain their maximum, at Ho- 
barton, also during the hours of the night, but with a small systematic 
difference as to the precise hour, and with this distinguishing pecu- 
liarity, that the deflection at Hobarton is'of the opposite pole of the 
needle (or of the same pole in the opposite direction) to the Toronto 
disturbance ; whilst at a third station, St. Helena, which is a tropical 
one, the hours of principal disturbance are those not of the night, 
but of the day. A very superficial examination is sufficient to show 
that for the generalization of the facts,—a generalization which is 
indispensable for their correct apprehension and employment in the 
formation of a theory,—the stations at which the phenomena are to 
be known must be increased. Those which were chosen for a first 
