VARIATION OF TERRESTRIAL MAGNETISM. 
491 
Table XVIII.—Observed and calculated values of and in the expression 
cos {t — + rg cos 2 for vertical force. 
Bombay. 
Lisbon. 
Greenwich. 
St. Petersburg, 1870 . . 
„ 1878. . 
n- 
Calculated 
from inside. 
Calculated 
from outside. 
Observed. 
Calculated 
from inside. 
Calculated 
from outside. 
1 
Observed. 
226 
491 
398 
235 
144 
346 
269 
142 
43 
176 
65 
169 
30 
171 
333 
143 
77 
132 
277 
112 
53 
35 
1.53 
51 
71 
24 
The agreement between the calculated and observed curves for vertical force is best 
seen from the graphical representation given in figs. 7, 8, 9, 10. In the curves, the 
diurnal and semidiurnal variation only have been taken into account. It is seen 
how at Bombay, Lisbon, and Greenwich the observed curves are almost identical in 
shape with the curves calculated on the hypothesis of an external cause, if the range 
is reduced in a proper ratio. The disagreement with the curves calculated on the 
other alternative is complete, a maximum occurring where a minimum should occur, 
and vice versd. At St. Petersburg, although the agreement is much worse, the 
1878 curve, which has been corrected for temperature, follows pretty closely the shape 
of the calculated curve. The numbers from which the curves have been drawn are 
given in Table XIX. 
Fig. 7. 
Bojibay. 
Comparison between calculated and observed curve of vertical force. The abscissm denote astronomical 
time, the ordinates vertical force, the unit of force being C.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. 
3 R 2 
