578 Tables 730 and 731 (charts) 



TERRESTRIAL MAGNETISM 



TABLE 730. — World Isoporic Lines for / (Lines of Equal Annual Change) 

 Approximate Epoch 1920-1925 



TABLE 731. — World Isoporic Lines for H (Lines of Equal Annual Change) 

 Approximate Epoch 1920-1925 



Smithsonian Tables 



