ON THE MAGNETIC DISTURBANCES. 493 



separately by each of the three magnetic elements, and 

 has been evidenced alike wherever observations have 

 been maintained for a sufficient time to include the two 

 opposite epochs of the period, and have been submitted 

 to a suitable process of examination. 



The primary connection of the disturbances with the 

 sun is evidenced also by the discovery, (which has been 

 another result of the mode of investigation referred to), 

 that their mean effects, in all parts of the globe and in 

 each of the elements, are found to be invariably governed 

 by periodical laws, whose period is a mean solar day. 

 This is the one feature which is constant, amidst diver- 

 sities in the hours of maximum and minimum of the 

 different elements at the same station, and of the same 

 element at different stations, diversities which fully 

 account for the absence of absolute correspondence in the 

 simultaneous movements of the magnetometers at places 

 distant from each other, and harmonise with the con- 

 jecture of the contemporaneous existence of more than 

 a single force. It is in this view especially to be noticed 

 that, at the same station, the disturbances which pro- 

 duce easterly deflections of the declination, and those 

 which produce westerly deflections of the same, have 

 distinctly different laws ; as have also the disturbances 

 which increase and those which decrease the inclination, 

 as well as those which increase and those which decrease 

 the intensity of the magnetic force. The laws are in 

 all these cases highly systematic, the hours of maximum 

 and minimum well marked, and the progression regular. 

 There are thus, at each station, six distinct phenomenal 

 laws of this particular class of phenomena coexisting, 

 and necessarily producing much complexity by their 



