VARIATION OP TERRESTRIAL MAGNETISM. 
493 
Pig. 9. 
Greenwich. 
Comparison between calculated and observed curve of vertical force. The abscissae denote astronomical 
time, the ordinates vertical force, the unit of force being O.G.S. 10”®. 
Observed curve, white line. Curve calculated on hypothesis of outside force, dotted line. Curve 
calculated on hypothesis of inside force, white and black line. 
Pig. 10. 
St. Petersburg. 
Comparison between calculated and observed curve of vertical force. The abscissae denote astronomical 
time, the ordinates vertical force, the unit of force being C.G.S. 10~®. 
Observed curves, white line—I. for 1870, II. for 1878. Curve calculated on hypothesis of outside force, 
dotted line. Curve calculated on hypothesis of inside force, white and black line. 
