M \ G N E T 1 (' S D I! V E V I' V E N N S Y L V A » I \ 



79 



The next and last hypothesis, 



X= 3.900 — 0.1934 dL + 0.01:51 dMcos L, 

 in which the isodynamic lines are treated as straight lines presents, perhaps, the 

 best and most simple expression of the irregular distribution of the horizontal 

 force. These lines run nearly parallel with the dip lines. 



The difference between the lines of this and the previous hypothesis shows tli • 

 large amount of local irregularity. 



The lines of this hypothesis pass through the following positions: — 



4.2 



4.0 

 3.8 

 3.6 



Long. 81°. 

 Lat. :;'.i°58' 



Long. 81°.0 

 Lat IP or 



Long. 81°.0 

 Lat. 12°02' 

 Long. 81°.0 

 Lat. I:; "I 



Long. 77°.5 

 Lat. 39° 41' 

 Long. 7 7°. 5 

 Lat. lo=49' 

 Long. 77°.5 

 Lat. il 51 

 Long, 77 .5 

 Lat. 12 



Long. 74°.0 

 Lat. 39° 36' 

 Long. 74°.0 

 Lat. 40° 39' 

 Long. 74°.0 

 I. ;il. 11 ° 41' 

 Long. 71°.0 

 Lat. 42 l.;' 



