64 



point in the direction of its axis, and lengthen the line at 

 the same time and perform this operation for every 20the 

 degree on the earth-equator, we will have another systeme 

 of lines (introduced by Duperrey) called magnetic meri- 

 dians. These lines, alike the astronomic meridians but not 

 congruent with them, meet all in two points, the one situa- 

 ted in the north hemisphere at about lat. 73° 35' and long. 

 264° 21', the other in the south hemisphere at (south) lat. 

 72° 35' and long. 152° 30'*). 



Both these systems of lines are represented on the 

 figure 1 for the north hemisphere and in 2 for the south. 



If we now unite all points where the intensity of the 

 total magnetic force is the same, we shall have a new sy- 

 steme of parallels represented in the figure 3 for the nor- 

 thern and in fig. 4 for the southern hemisphere, less regu- 

 lar than the first but however with the general eharacter 

 of parallel-circles. 



These systemes of lines nothwithstanding many irre- 

 gularities, show by their general corse that the force they 

 represent is one and the same över the whole earth-sur- 

 face or in other words that all the magnetic phenomena 

 we observe on the globe belong to an unique system of 

 energy. The earth can best be compared with a magnetic 

 sphere, the magnetic matter of which is not equally distri- 

 buted in its body and in which the magnetising force forms 

 an angle of about 17° with the rotation-axis. 



To our knowlegde of this magnificent system, the unity 

 of which is unmistakable, all ihe civilizised nations have 

 contributed, but in much different degrees. The greatest 

 part is given by the navigating nations and among them 

 the English nation occupies the first place. 



One of the most beautiful contributions is given by 

 Gauss, who showed that the whole system could be repre- 

 sented by a mathematic formula. The constants in this 



*) East fr. Greenwich. 



