POLAR LIGHT, OR AUllOKA. 161 



vibration of magnetic needles. In this manner, by 

 comparison of the specific weight, and by applying the 

 microscope to finely pulverised portions, it may be 

 decided whether the strength of the polarity does not 

 often proceed less from the quantity of the interspersed 

 grains of magnetic iron and iron oxide, than from the 

 relative position of the grains. A more important 

 question, however, in cosmical respects, and which was 

 propounded by me long since in connection with the 

 Haidberg, is: whether there are mountain-ridges in 

 which an opposite polarity is found on the opposite 

 sides ? ( 224 ) An accurate astronomical determination of 

 the magnetic axis of such a mountain would become of 

 great interest, if after considerable intervals of time 

 there should be recognised either an alteration in the 

 direction of the axis, or an (at least apparent) indepen- 

 dence of the three variable elements of the general 

 magnetic force of the earth. 



VOL. IT. M 



