ON BRITISH COLONIAL MAGNETIC OBSERVATORIES. 363 
intermission. So far they have still appeared to justify the term irre¬ 
gular which had been originally applied to them. But on a more close 
and studious examination, and by adopting a prooess of investigation suit¬ 
able for the purpose, the frequency with which disturbances of this unex¬ 
plained character occur, and the aggregate amount of disturbance which 
they produce in the different mouths of the solar year and at the different 
hours of the solar day, were found to exhibit periodical laws of consistent 
and steady recurrence. In the case of the hours, for example, and confining 
the attention to a single station on the globe, it was found, by concurrent 
results in each of several successive years, that, the greatest amount of dis¬ 
turbance occurred at a certuin hour, ami the least amount at another certain 
hour; and that this was the case both in the direction and the force, though 
not at the same hours; aUo, that the disturbances which increase the force 
had certain hours of maximum and minimum, and those which diminish the 
force certain other hours of maximum and minimum ; and that, in n similar 
manner, the disturbances deflecting the needle in one direction Imd their 
lixed hours of maximum and minimum, and those detecting the needle in 
the opposite direction bad also their own particular hours. It need scarcely 
be said that laws which, os may easily be supposed, arc somewhat complicated 
in their results, are nut obvious in every disturbance that occurs; but certi¬ 
tude in respect to the stated regularity of their occurrence is obtained by the 
employment of the method which has been so fertile of late years in the 
establishment of so many natural laws, viz, the deduction of mean numerical 
values from a large body of observations, and the subsequent comparison 
of these with the mean values corresponding to distinct parts of the same. 
I»y the adoption of this method, the periodical fluctuation of which we are 
speaking i» found to take place with great regularity at all the stations 
at which the investigation has yet been made. The progressions from the 
maxima to the minima and from the minima to the maxima are almost 
uniformly continuous in the results, even of each independent year; thus 
manifesting an existing connexion between the disturbances and the hours of 
solar time. By the same method, a similar periodicity is shown to exist in the 
disturbances occurring in the different months which constitute the solar year. 
At all the stations where the investigation has hitherto been made, the 
disturbances are thus found to manifest periodical laws dependent on the 
s'dar hours and the solar mouths. The epochs of the maxima and minima 
0 l| ie‘several phenomena lire not the same at different stations; and for the 
complete elucidation of the subject a greatur number of stations will there- 
ore bo required than those at which the examination has yet been made, 
ut for our present purpose wo have full and sufficient evidence, that whilst 
0,1 le (IIIt ‘ hand the disturbances occur from time to time at intervals which 
are 1101 mar ked by any other ordinary terrestrial phenomena with which 
"e arc acquainted, they manifest, at the same lime, in their details a sub- 
orawiatioii to solar times which shows them to have a connexion of some 
ini with the sun. Now, if thin connexion could be traced no further, it 
'gut be difficult absolutely to establish, that the effects, which have been 
ms described, were notin some way dim to those variations of temperature 
card 'n * Un occ . as ' ons *** the atmosphere anil ut the surface of the 
the I conr| cxion, however, between the frequency and the amount of 
to wT’T ai| d tbe ^frequency amt amount of the magnetic disturbances, 
’ lien I now proceed, appears to offer no uncertainty, and to admit of no 
’ t 1 , dus nature; for the most careful investigations by physicists of 
of th em,D . 0,l . Ce a,l(l e *pe«ence have failed to discover the slightest influence 
le variations of the solar spots upon the thermic conditions either of 
