TERRESTRIAL MAGNETISM. 



295 



sity. Thus, in England the horizontal intensity is about 0.17 

 gauss, and in Florida the horizontal intensity is about 0.30 gauss. 



180 160 . 120 SO 60 



30 60 90 120 150 180 



180 1 120 90 60 30 30 CO 90 120 150 180 



Fig. 4. 

 Lines of equal magnetic inclination. 



120 90 60 30 30 .CO 90 120 150 



150 120 90 00 80 30 00 90 120 150 



Fig. 5. 

 Lines of equal horizontal intensity. 



6. Variations of the earth's magnetic field. Each one of the 

 magnetic elements, declination, inclination, and horizontal inten- 

 sity, is subject to variations of four distinct kinds, as follows : 



