G. Sack: lieber die tägliche, jährliche und elfjährige Periode etc.
5
Nur die Zahlen der 5. Spalte sind für die Jahre 1883—1887 den „Results of Greenwich Observations“
Tabelle IX Spalte 2 entnommen, alle übrigen Angaben sind mir von Herrn Christie mit folgendem Begleitschreiben
mitgetheilt worden:
„ further details are given concerning methods of working up the results, applying
them to reduction of the observations for 1887.
The mean of the twelve monthly Horizontal Force ordinates by the registering instrument
in the year 1887 for the times corresponding to the observations of absolute horizontal force is
517, the mean of the corresponding twelve observed values of absolute horizontal force being
1.8175. Taking the difference between the mean ordinate 517 and the several mean monthly
values given in Table XI of the printed volume we obtain differences for each month which
multiplied by 1.8175 give corrections to the mean yearly observed absolute horizontal force, by
application of which mean monthly values are found as follows.
Mean monthly
Horizont. Force
Table XI
Excess
above 517
Excess X 1.8175
= correction
to 1.S175
Mean monthly
value of
Horizont. Force
467
-50
- 9
1.8166
471
-46
- S
1.8167
483
-34
- 6
1.8169
521
+ 4
+ 1
1.8176
5S0
+63
+11
1.8186
553
+36
+ 7
1.8182
597
+80
+15
1.8190
547
+30
+ 5
1.S1S0
607
+90
+16
1.8191
557
+40
+ 7
1.8182
533
+16
+ 3
1.8178
432
—85
-15
1.S160
Mean 1.8177
Or we may take the twelve monthly horizontal force ordinates by the registering instrument
for the times corresponding to observations of absolute horizontal force and take the difference
between each and the corresponding mean monthly values (Table XI) so obtaining a correction
which multiplied by 1.8175 gives for each month a correction to the observed value of absolute
horizontal force, by application of which mean monthly values are found.
HorizontalForce ordinate
by registering instrument
at time of observation
of absolute horizont. force
Monthly
value
Table XI
Correction
Corr.
X 1.8175
Observed
absolute
value
Mean
monthly
value
391
467
+ 76
+14
1.8145
1.8159
460
471
+ 11
+ 2
1.8125
1.8127
489
483
- 6
- 1
1.S148
1.8147
508
521
+ 13
+ 2
1.8175
1.8177
593
580
- 13
_ 2
1.8182
1.8180
663
553
-110
-20
1.8218
1.8198
611
597
- 14
— 3
1.8184
1.8181
635
547
- 88
-16
1.8204
1.8188
682
607
— 75
-14
1.8205
1.8191
463
557
+ 94
+17
1.8176
1.8193
400
533
+133
+24
1.8179
1.8203
313
432
+ 119
+22
1.8164
1.8186
Mean 1.S177
The two methods should give the same results. The first depends on the steadiness of the
bifilar magnet through the year, in the second any accidental error in the determination of any
