IN THE MEAN EFFECTS OF THE LARGER MAGNETIC DISTURBANCES. 373 
signs in no case equals zero, but has a sensible magnitude in each element, the 
absolute values of these elements must also be affected with a very small cyclical 
variation due to the disturbances, of which the period will also be quinquennial. 
In concluding this paper, I may venture to congratulate the Royal Society on the 
success which has attended the attempt, commenced at its recommendation and 
carried out under its auspices, to investigate the laws of these remarkable and 
mysterious phenomena, the Magnetic Disturbances, by the philosophical method of 
extensive and systematic observation ; and on the proof which this paper contains of 
the sufficiency for their purposes of the instrumental means devised by the Com- 
mittee of Physics for observing the variations of the Horizontal and Vertical Forces ; 
and of which, especially in regard to the Vertical Force magnetometer, doubts have 
been sometimes expressed, arising apparently in some cases from the want of sufficient 
skill in the artist who attempted to construct the instrument, and in others from the 
absence of any personal experience in those who expressed opinions as to its probable 
performance. By means of these two instruments, a full confirmation has now been 
given to the existence of periodical laws of systematic order and regularity in pheno- 
mena previously regarded as irregular, the periodical character of the decennial, 
annual and diurnal variations being as clearly shown by the disturbances of the 
Inclination and Total Force as by those of the Declination; thus accomplishing the 
first important step towards a physical theory of the Disturbances by the direct 
connexion which they are now shown to have with the Sun. 
The conclusions which can be drawn from the observations at a single station are 
necessarily limited to the theory of the phenomena as they present themselves at a 
single point on the earth’s surface. May it not be hoped, that the fruits which have 
recompensed the labour bestowed on the Toronto observations, may encourage some 
amongst the numerous physicists in Europe and America, who signified their desire 
to cooperate with the Royal Society in this inquiry, and to adopt the methods and 
processes of observation which have been followed out at Toronto, to apply them- 
selves to the deduction of fhe laws of the occasional disturbances which, from the 
example of Toronto, they may expect to be able to disentangle from the great mass 
of observations on which their labour has been already bestowed; provided that 
those observations have been made with the care and perseverance which have 
distinguished those made by the Officers and Non-commissioned Officers of the 
Royal Artillery at the Toronto Observatory? Few may be willing to face a heavy 
labour of reduction before experience has shown that results will follow from the 
labour ; but some may be expected to do so when an example is before them that 
this additional labour bestowed on their observations will not be without its recom- 
pense : a very few stations at which the investigation should be as full and as satis- 
factory as at Toronto, might, if widely distant from each other on the earth’s surface, 
suflSce to form a general theory of the phenomena of the magnetic disturbances. 
The observations at the St. Helena and Hobarton observatories are undergoing a 
MDCCCLVI. 3 D 
