83 COSMOS. 



ticipate in the production and manifestation of magnetic 

 phenomena. 



If, according to Newton's view, it is very probable that 

 the substances which belong to a group of celestial bodies (to 

 one and the same planetary system) are for the most part 

 identical, 8T we may from inductive reasoning conclude that 

 the electro-magnetic activity is not limited to the gravi- 

 tating matter on our own planet. To adopt a different 

 hypothesis would be to limit cosmical views with arbitrary 

 'dogmatism. Coulomb's hypothesis regarding the influence of 

 the magnetic sun on the magnetic earth is not at variance 

 with analogies, based upon the observation of facts. 



If we now proceed to the purely objective representation 

 of the magnetic phenomena, which are exhibited by our 

 planet on different parts of its surface, and in its different 

 positions in relation to the central body, we must accurately 

 distinguish, in the numerical results of our measurements, 

 the alterations which are comprised within short or very 

 long periods. All are dependent on one another, and in this 

 dependence they reciprocally intensify, or partially neutralize 

 and disturb each other, as the wave-circles in moving fluids 

 intersect one another. Twelve objects here present them- 

 selves most prominently to our consideration. 



Two magnetic poles, which are unequally distant from the 

 poles of rotation of the earth, and are situated one in each 

 hemisphere ; these are points of our terrestrial spheroid at 

 which the magnetic inclination is equal to 90, and at which 

 therefore the horizontal force vanishes. 



The magnetic equator, the curve on which the inclination 

 of the needle = 0. 



The lines of equal declination, and those on which the 

 declination =. (isogonic lines and lines of no variation). 



Tlie lines of equal inclination (isoclinal lines). 



The four points of greatest intensity of the magnetic force, 

 two of unequal intensity in each hemisphere. 



The lines of equal terrestrial force (isodynamic lines). 



The undulating line which connects together on each 

 meridian the points of the weakest intensity of the terrestrial 

 force, and which has sometimes been designated as a dynamic 



97 Cosmos, vol. i, pp. 122, 123 ; also vol. iv, p. 568. 



