468
THE HONGKONG GOVERNMENT GAZETTE, 29TH MAY, 1886.
H
Value of 1 +
F
TABLE III.
for different values of the deflection produced by a twist of 90° of the suspending thread.
Effect of 90° torsion.
H
1+
F
0.25 div.
1.00008
0.50
1.00017
0.75
1.00025
1.00
1.00034
1.25
1.00043
1.50
1,00052
1.75
1.00060
2.00
1.00068
2.25
1.00077
2.50
1.00086
2.75
1.00094
3.00
1.00103
TABLE IV.
Reduction to 0°
t
qt + q' t2
t
qt + q' t2
+ 14°
+.00412
+ 27°
+.00881
15
.00446
28
00920
16
.00480
29
.00960
17
.00514
30
.01001
18
.00549
31
.01042
19
:00584
32
.01084
20
.00619
33
.01126
21
.00655
34
.01168
22
.00692
35
.01211
23
.00729
36
.01254
24
.00766
37
.01297
25
.00804
38
.01341
26
.00842
39
.01385
+ 27
.00881
+ 40
.01430
TABLE V.
Value of logr3 at different temperatures.
t
r = 30
ro -
40
.00
4.13033
4.50515
4.13045
4.50527
10
4.13057
4.50538
15
4.13069
4.50550
20
4.13080
4.50562
25
4.13092
4.50574
30
4.13104
4.50585
35
4.13116
4.50597
40
4.13127
4.50609
On the determination of the declination.
The zero or true north point on the horizontal circle of the magnetometer is ascertained as follows from observations of Polaris. The horizontality of the axis of the speculum having been verified th speculum is placed vertically and revolved round its vertical axis till the image of the wires, a high are illuminated by a lamp held beside the collimating eye-piece of the telescope, appears in the held. The speculum is turned by its slow motion screw till the image of the vertical wire is covered by the latter itself. The instrument is then revolved round its vertical and the speculum round its horisontal axis till the image of Polaris is bisected by the wires, and both verniers of the circle are then read. This operation is repeated after reversing the mirror on its pivots. The speculum is then turned half a circumference round its vertical axis and the operation repeated directly and again after reversing the mirror on its pivots. The image of the vertical wire is therefore four times covered by the wire.
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