MAGNETIC DECLINATION AT KEW AND NEBTSCHINSK. 
241 
a connexion subsisting between the points of terrestrial origin of the disturbances, and 
the Poles or Points of maximum force of the two systems which conjointly determine 
the distribution of the magnetic influence on the globe, has been examined, and to some 
extent strengthened. We have now to await the concurrent evidence which may result 
from a similar examination of the disturbances of the Dip and of the Total Force, which 
it is hoped may appear in a continuation of the papers on the results obtained at the 
Kew Observatory. But for the completion of the retrospective view of the progress 
which has been made in developing the theory of the magnetic disturbances, and in 
conducting us possibly to a more perfect knowledge of the general causes of terrestrial 
magnetism than we previously possessed, I must revert to the remark occurring in the 
earlier part of this paper (page 232), that the value adopted for each element and at 
each station to characterize what should be regarded as a disturbed observation, was 
purposely made a 'constant amount , with a view to an examination of the relative amount 
of disturbance in different months and in different years. It was in this way learnt, as is 
stated in the second volume of the Toronto Observations, pp. xxii and xxiii, that “1843, 
1844, and 1845 were years in which the proportion of observations affected by a certain 
constant amount of disturbance was much smaller than the preceding years 1841 and 
1842, or the following years, 1846, 1847, and 1848;” presenting thus the aspect of a 
periodical variation of which the epoch of minimum might be assigned to the years 
1843 and 1844, but of which the period or cycle had yet to be learnt. The phenomena 
were not peculiar to a single station, but were found to correspond in localities most 
distant from each other : nor were they confined to one only of the magnetic elements, 
but were exhibited by all, each element having its own distinct instrumental means of 
measurement. They were therefore recognized as the indication of a magnetic affection 
common to the whole of our globe, constituting a periodical variation in the amount of 
disturbance in different years. In 1851 and 1852 the annual ratios of disturbance were 
found to be everywhere decidedly on the decrease , the epoch of maximum appearing to 
have taken place in 1848-1849. The evidence of the existence of a decennial variation 
appearing to be thus complete, its announcement, as a fact of which the knowledge was 
acquired by a process of investigation specially designed for the discovery of any such 
periodical variation, if one should exist, was on the. point of taking place, when a fortu- 
nate incident (the receipt from M. de Humboldt of a proof-sheet of his ‘ Kosmos,’ con- 
taining the first publication of Hofrath Schwabe’s Table of the variations of the solar 
spots from 1826 to 1850) brought to my knowledge the existence of a corresponding 
variation in the physical aspect of the sun, precisely similar in period and epochs to 
the terrestrial magnetic variation. The importance of a revelation which gave a present 
apparent connexion, and presented the promise of establishing a permanent connexion, 
between the previously isolated terrestrial magnetic phenomena and the physical affec- 
tions of the central body of our system, could not well be overrated. It was not alone 
the cosmical character which it imparted to a single terrestrial magnetic variation other- 
wise unconnected and inexplicable, — but there could scarcely fail to be impressed on the 
