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enough has been already stated to show the magnitude, the regula- 

 rity, and the systematic character of the changes called secular, 

 which are thus produced by forces in constant operation at the sur- 

 face of our planet. In our entire inability to connect these changes 

 with any other of the phenomena of nature, either cosmical or ter- 

 restrial, we appear to have no other alternative than to view them as 

 a constituent feature of the terrestrial magnetic force itself, and as 

 one of its most remarkable characteristics, not to be overlooked by 

 those who would seek to explain the phenomena of that force by 

 means of a physical theory. The attempts which have sometimes 

 been made to explain them by a supposed connection of the ter- 

 restrial magnetic phenomena with the distribution of land and sea at 

 the surface of the globe, or with the distribution of heat on that 

 surface, or by electrical currents excited by the rotation of the earth 

 on its axis, contain no provision to meet a systematic variation of 

 this nature ; and break down altogether when the facts of the secu- 

 lar change are duly apprehended. From the phenomena of a single 

 element at a single station, as here presented, we may assure 

 ourselves that effects proceeding with so much order and regularity, 

 which we cannot ascribe to any other cause than that of the ter- 

 restrial magnetism itself, and cannot therefore separate from its other 

 manifestations, must find a place in any physical theory which pro- 

 fesses to explain the phenomena of the earth's magnetism. To learn 

 the changes in this and in the other magnetic elements which are 

 simultaneously in progress in other parts of the globe, and to appre- 

 hend their mutual connexion and the general system of secular 

 change which they indicate, it is necessary that the facts should be 

 collected in the same manner as at St. Helena, at a great number of 

 stations distributed over the earth's surface, and that they should be 

 studied both separately and together. This may indeed appear a 

 work of labour ; but it is the most certain, if not the only certain 

 mode of arriving at a correct knowledge of phenomenal laws, when 

 the laws of their causation are wholly unknown. In this, as in simi- 

 lar studies, however complex the phenomena may appear at the first 

 aspect, and it is fully admitted that those of the secular magnetic 

 change do appear extremely complex at the first view, the mind 

 soon begins to recognize order amidst apparent irregularity, and 

 system amidst incessant variation. The order and regularity with 



