80 COSMOS. 



of a two-fold object. The greater number of these labors 

 have been devoted to the observation of the magnetic activi- 

 ty of our planet in its numerical relations to time and space, 

 while the smaller part belongs to experiments, and to the 

 manifestation of phenomena which promise to lead us to the 

 knowledge of the character of this activity, and of the in- 

 ternal nature of the magnetic force. Both these methods — 

 the numerical observation of the manifestation of terrestrial 

 magnetism, both in respect to its direction and intensity — 

 and physical experiments on the magnetic force generally, 

 have tended reciprocally to the advancement of our physical 

 knowledge. Observations alone, independently of every hy- 

 pothesis regarding the causal connection of phenomena, or 

 regarding the hitherto immeasurable and unattainable recip- 

 rocal action of molecules in the interior of substances, have 

 led to important numerical laws. Experimental physicists 

 have succeeded, by the display of the most wondrous inge- 

 nuity, in discovering in solid and gaseous bodies polarizing 

 properties, whose presence had never before been suspected, 

 and which stands in special relation to the temperature and 

 pressure of the atmosphere. However important and un- 

 doubted these discoveries may be, they can not, in the pres- 

 ent condition of our knowledge, be regarded as satisfactory 

 grounds of explanation for the laws which have already been 

 recognized in the movements of the magnetic needle. The 

 most certain means of enabling us thoroughly to comprehend 

 the variable numerical relations of space, as well as to ex- 

 tend and complete that mathematical theory of terrestrial 

 magnetism which was so nobly sketched by Gauss, is to pros- 

 ecute simultaneous and continuous observations of all the 

 three elements of the magnetic force at numerous well-se- 

 lected points of the earth's surface. I have, however, else- 

 where illustrated, by example, the sanguine hopes which I 

 entertained of the great advantages that may be derived from 

 the combination of experimental and mathematical investi- 

 gation.* 



Nothing that occurs upon our planet can be supposed to 

 be independent ot cosmical influences. The word planet in- 

 stinctively leads us to the idea of dependence upon a central 

 body, and of a connection with a group of celestial bodies 

 of very different masses, which probably have a similar or- 

 igin. The influence of the sun's position upon the manifest- 

 ation of the magnetic force of the earth was recognized at a 



* See p. 10. 



