mi. A. W. RUCKER AND DR. T. E. THORPE ON A MAGNETIC 
ns 
Date. 
Deflection. 
Vibration. 
H. 1 
Vy 
Ai. 
v^. 
^2- 
Observed. 
Corrected. 
September .30 ... . 
+ 7 
0 
+ 3 
0 
1-8117 
1-8112 
October 11. 
2 
0 
- 2 
0 
1-8114 
1-8114 
„ 12. 
3 
- 20 
- 1 
- 20 
1-8096 
1-8115 
„ 13. 
- .5 
- 20 
- 10 
- 10 
1-8092 
1-8114 
„ 18. 
- 5 
0 
- 13 
0 
1-8114 
1-8123 
, 18. 
— 5 
0 
- 11 
0 
1-8117 
1-8125 
„ 19. 
- 4 
- 10 
- 10 
0 
1-8113 
1-S125 
As then the diurnal variation between the hours at which our observations were 
generally taken amounts to 0'0025 metric unit, and as the probable difierence 
between the corrected semi-independent results at the stations referred to in Table I., 
p. 67, is "0004 (the probable error being half that quantity), and as the probable error 
of the seven Kew observations is less than ’0004, there seems no doubt that the 
correction ought to be applied. 
In the case of the Dip the diurnal range (which is more than 2') exceeds the error 
of experiment, but the application of a correction for disturbance is more difficult and 
uncertain. It has to be deduced from the Vertical and Horizontal Force magneto- 
grams and thus the chances of error are increased. The quantities to be dealt 
with are generally small, and the uncertainty of the readings taken from the curves 
unquestionably affects the results. V/e have not many data which furnish any a 
2:)OSteriori arguments of importance, as in most cases the times at which the two Dip 
observations were taken were separated by too short an interval for the diurnal 
variation to have altered much. The observations made at Kew in 1887 are, however, 
decidedly improved by correction. 
Date. 
Instru¬ 
ment. 
Needle. 
Dip 
observed. 
V. 
A. 
Dip 
corrected. 
September 30 ... . 
74 
1 
67 35-4 
- 0-7 
+ 0-7 
0 / 
67 35-4 
74 
2 
34-7 
- 0-8 
+ 1-3 
34-2 
October 11. 
83 
1 
67 33-8 
- 0-4 
0 
67 34-2 
83 
2 
34-9 
- 0-5 
0 
35-4 
,, 13. 
83 
1 
67 36-0 
- 0-4 
-b 1-4 
67 35-0 
83 
2 
36-1 
- 0-5 
+ 1-6 
35-0 
18. 
83 
1 
67 .34-2 
- 0-3 
-b 0-3 
67 34-2 
83 
2 
34-2 
- 0-4 
-b 0-3 
34-3 
„ 19 . 
74 
1 
67 35-0 
- 0-3 
0 
67 35-3 
74 
2 
33-5 
— 0-3 
- 0-7 
34-5 
The greatest differences in the corrected and uncorrected results are T‘2 and 2'*G 
respectively. 
